Partially and fully surface-enabled transition metal ion-exchanging energy storage devices

ABSTRACT

A surface-enabled, metal ion-exchanging battery device comprising a cathode, an anode, a porous separator, and a metal ion-containing electrolyte, wherein the metal ion is selected from aluminum (Al), gallium (Ga), indium (In), tin (Sn), lead (Pb), or bismuth (Bi), and at least one of the electrodes contains therein a metal ion source prior to the first charge or discharge cycle of the device and at least the cathode comprises a functional material or nanostructured material having a metal ion-capturing functional group or metal ion-storing surface in direct contact with the electrolyte. This energy storage device has a power density significantly higher than that of a lithium-ion battery and an energy density dramatically higher than that of a supercapacitor.

CROSS REFERENCE TO RELATED APPLICATIONS

The present application is a continuation application of U.S. patentapplication Ser. No. 14/121,050 filed Jul. 25, 2014 (U.S. PatentPublication No. 2016/0028122), which is a divisional application of U.S.patent application Ser. No. 12/930,294 filed Jan. 3, 2011 (now U.S. Pat.No. 8,859,143 issued Oct. 14, 2014) the contents of which areincorporated by reference herein, in their entirety, for all purposes.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

This invention is based on the research results of a project sponsoredby the U.S. National Science Foundation SBIR-STTR Program and the U.S.Government may, therefore, have certain rights in the invention(s)described herein.

FIELD OF THE INVENTION

The present invention relates generally to the field of electrochemicalenergy storage devices and, more particularly, to a totally new metalion-exchanging battery device wherein the operation of either thecathode or both the anode and the cathode is intercalation-free (i.e.does not involve metal ion diffusion in and out of the bulk of a solidelectrode-active material). The metal ions are exchanged between ananode active material and a cathode active material during charge ordischarge cycles. The metal ion storage mechanism in either the cathodeor both the anode and the cathode is electrode active materialsurface-controlled or, more accurately, “surface-mediated” or“surface-enabled”, obviating the need for solid-state diffusion(intercalation and de-intercalation) of metal atoms or ions, whichotherwise is very slow. This device has the high energy density of amodern battery and a power density that is orders of magnitude higherthan those of lithium-ion batteries. The power density is even higherthan those of conventional supercapacitors. This device is hereinreferred to as a surface-controlled or surface-enabled, metalion-exchanging battery device. The metal ion is selected from alkalimetals (not including lithium alone), alkaline-earth metals, transitionmetals, and other metals (e.g., aluminum, gallium, indium, tin, bismuth,and lead).

BACKGROUND OF THE INVENTION

Supercapacitors (Ultra-Capacitors or Electro-Chemical Capacitors):

Supercapacitors are being considered for electric vehicle (EV),renewable energy storage, and modern grid applications. The highvolumetric capacitance density of a supercapacitor (10 to 100 timesgreater than those of electrolytic capacitors) derives from using porouselectrodes to create a large surface area conducive to the formation ofdiffuse double layer charges. This electric double layer (EDL) iscreated naturally at the solid-electrolyte interface when voltage isimposed. This implies that the specific capacitance of a supercapacitoris directly proportional to the specific surface area of the electrodematerial, e.g. activated carbon. This surface area must be accessible byelectrolyte and the resulting interfacial zones must be sufficientlylarge to accommodate the EDL charges.

This EDL mechanism is based on surface ion adsorption. The required ionsare pre-existing in a liquid electrolyte and do not come from theopposite electrode. In other words, the required ions to be deposited onthe surface of a negative electrode (anode) active material (e.g.,activated carbon particle) do not come from the positive electrode(cathode) side, and the required ions to be deposited on the surface ofa cathode active material do not come from the anode side. When asupercapacitor is re-charged, local positive ions are deposited onto orclose to a surface of a negative electrode with their matting negativeions staying close side by side (typically via local molecular or ionicpolarization of charges). At the other electrode, negative ions aredeposited onto or close to a surface of this positive electrode with thematting positive ions staying close side by side. Again, there is noexchange of ions between an anode active material and a cathode activematerial.

In some supercapacitors, the stored energy is further augmented bypseudo-capacitance effects due to some electrochemical reactions (e.g.,redox). In such a pseudo-capacitor, the ions involved in a redox pairalso pre-exist in the same electrode. Again, there is no exchange ofions between an anode active material and a cathode active material.

Since the formation of EDLs does not involve a chemical reaction or anexchange of ions between the two opposite electrodes, the charge ordischarge process of an EDL supercapacitor can be very fast, typicallyin seconds, resulting in a very high power density (typically5,000-10,000 W/kg). Compared with batteries, supercapacitors offer ahigher power density, require no maintenance, offer a much highercycle-life, require a very simple charging circuit, experience no“memory effect,” and are generally much safer. Physical, rather thanchemical, energy storage is the key reason for their safe operation andextraordinarily high cycle-life.

Despite the positive attributes of supercapacitors, there are severaltechnological barriers to widespread implementation of supercapacitorsfor various industrial applications. For instance, supercapacitorspossess very low energy densities when compared to batteries (e.g., 5-8Wh/kg for commercial supercapacitors vs. 10-30 Wh/kg for the lead acidbattery and 50-100 Wh/kg for the NiMH battery). Lithium-ion batteriespossess a much higher energy density, typically in the range of 100-180Wh/kg, based on the cell weight.

Lithium-Ion Batteries:

Although possessing a much higher energy density, lithium-ion batteriesdeliver a very low power density (typically 100-500 W/kg), requiringtypically hours for re-charge. Conventional lithium-ion batteries alsopose some safety concern.

The low power density or long re-charge time of a lithium ion battery isdue to the mechanism of shuttling lithium ions between an anode activematerial and a cathode active material, which requires lithium ions tointercalate into the bulk of anode active material particles duringre-charge, and into the bulk of cathode active material particles duringdischarge. For instance, as illustrated in FIG. 1(A), in a most commonlyused lithium-ion battery featuring graphite particles as an anode activematerial, lithium ins are required to diffuse into the inter-planarspaces of a graphite crystal at the anode during re-charge. Most ofthese lithium ions have to come all the way from the cathode side bydiffusing out of the bulk of a cathode active particle (e.g. lithiumcobalt oxide, lithium iron phosphate, or other lithium insertioncompound) through the pores of a solid separator (pores being filledwith a liquid electrolyte), and into the bulk of a graphite particle atthe anode. During discharge, lithium ions diffuse out of the anodeactive material, migrate through the liquid electrolyte phase, and thendiffuse into the bulk of complex cathode crystals.

These intercalation or diffusion processes require a long time toaccomplish because solid-state diffusion (or diffusion inside a solid)is difficult and slow. This is why, for instance, the currentlithium-ion battery for plug-in hybrid vehicles requires 2-7 hours ofrecharge time, as opposed to just seconds for supercapacitors. The abovediscussion suggests that an energy storage device that is capable ofstoring as much energy as in a battery and yet can be fully recharged inone or two minutes like a supercapacitor would be considered arevolutionary advancement in energy storage technology.

Partially Surface-Controlled Lithium Ion-Exchanging Batteries or LithiumSuper-Batteries:

Instead of using an inorganic lithium intercalation compound, such asLiCoO₂ and LiFePO₄, that requires lithium insertion into and extractionfrom the bulk of an inorganic particle (typically 100 nm-20 μm, but moretypically 1-10 μm in diameter), several attempts have been made to useorganic molecules or polymers as an electrode active material for thecathode (lithium metal alone as the anode). For instance, Le Gall, et alinvestigated Poly(2,5-dihydroxy-1,4-benzoquinone-3,6-methylene) as anorganic polymer cathode [T. Le Gall, et al. J. Power Sources, 119 (2003)316-320] and Chen, et al used Li_(x)C₆O₆ organic cathode, obtained froma renewable source, in a lithium ion battery [H. Chen, et al. “Frombiomass to a renewable Li_(x)C₆O₆ organic electrode for sustainableLi-ion batteries,” ChemSusChem, 1 (2008) 348-355]. In addition, X. Y.Han, et al. studied carbonyl derivative polymers [“Aromatic carbonylderivative polymers as high-performance Li-ion storage materials,” Adv.Material, 19, 1616-1621 (2007)] and J. F. Xiang, et al. studied acoordination polymer as a cathode [“A novel coordination polymer aspositive electrode material for lithium ion battery,” Crystal Growth &Design, 8, 280-282 (2008)].

Unfortunately, these organic materials exhibit very poor electronicconductivity and, hence, electrons could not be quickly collected orcould not be collected at all. Although these organic molecules containcarbonyl groups (>C═O) that could readily react with lithium ions(forming a redox pair), this redox mechanism was overwhelmed by the poorelectronic conductivity. As a result, the battery cells featuring theseorganic molecules exhibit poor power densities. Le Gall et al added alarge proportion of conductive acetylene black (typically 40-60% byweight) to partially overcome the conductivity issue; but, acetyleneblack significantly dilutes the amount of the active material. Further,the best achievable specific capacity of 150 mAh/g is far less than thetheoretical specific capacity of 705 mAh/g ofPoly(2,5-dihydroxy-1,4-benzoquinone-3,6-methylene).

Recently, more electrically conducting carbon nanotubes (CNTs)containing carbonyl groups were used by Lee, et al to replace theorganic molecules for use as a cathode material [S. W. Lee, et al, “HighPower Lithium Batteries from Functionalized Carbon Nanotubes,” NatureNanotechnology, 5 (2010) 531-537]. The significantly higher electronicconductivity of CNTs does serve to overcome the poor conductivityproblem of organic molecules. However, the CNT-based electrodes preparedby the layer-by-layer (LBL) approach still suffer from several technicaland economical issues. Some of these issues are:

-   -   (1) CNTs are known to be extremely expensive due to the low        yield, low production rate, and low purification rate commonly        associated with the current CNT preparation processes. The high        material costs have significantly hindered the widespread        application of CNTs.    -   (2) CNTs tend to form a tangled mass resembling a hairball,        which is difficult to work with (e.g., difficult to disperse in        a liquid solvent or resin matrix).    -   (3) The so-called “layer-by-layer” approach (LBL) used by Lee,        et al is a slow and expensive process that is not amenable to        large-scale fabrication of battery electrodes, or mass        production of electrodes with an adequate thickness (most of the        batteries have an electrode thickness of 100-300 μm). The        thickness of the LBL electrodes produced by Lee, et al (a noted        MIT research group) was limited to 3 μm or less.    -   (4) One might wonder how the thickness of the LBL CNT electrodes        would impact their performance. The data provided by Lee, et al        (e.g. FIG. S-7 of the Supporting Material of Lee, et al) show        that the power density dropped by one order of magnitude when        the LBL CNT electrode thickness was increased from 0.3 μm to 3.0        μm. The performance is likely to drop even further if the        electrode thickness is increased to that of a useful battery or        supercapacitor electrode (e.g., 100-300 μm).    -   (5) Although the ultra-thin LBL CNT electrodes provide a high        power density (since Li ions only have to travel an extremely        short distance at the cathode), Lee, et al showed that the        CNT-based composite electrodes prepared without using the LBL        approach did not exhibit particularly good performance.    -   (6) CNTs have very limited amount of suitable sites to accept a        functional group without damaging the basal plane or graphene        plane structure. A CNT has only one end that is readily        functionalizable and this end is an extremely small proportion        of the total CNT surface. By chemically functionalizing the        exterior basal plane, one could dramatically compromise the        electronic conductivity of a CNT.

Most recently, our research groups have reported, in two patentapplications, the development of lithium ion-exchanging super-batteriesand two new classes of highly conducting cathode active materials foruse in these super-batteries. Each class of cathode active material hasa functional group that is capable of rapidly and reversibly forming aredox reaction with lithium ions. These materials are nanographene (bothsingle-layer graphene and multi-layer graphene sheets, collectivelyreferred to as nanographene platelets, NGPs) and disordered carbon(including soft carbon and hard carbon). These two patent applicationsare: C. G. Liu, et al., “Lithium Super-battery with a FunctionalizedNano Graphene Cathode” (US Patent Publication No. 2012/0045688, filedAug. 19, 2010) and C. G. Liu, et al, “Lithium Super-battery with aFunctionalized Disordered Carbon Cathode” (US Patent Publication No.2012-0077080, filed Sep. 23, 2010).

These new types of cathode active materials (used in the so-calledlithium super-battery or, in the present context, a partiallysurface-controlled lithium ion-exchanging battery) include a chemicallyfunctionalized nanographene platelet (NGP) or a functionalizeddisordered carbon material (such as soft carbon and hard carbon) havingcertain specific functional groups capable of reversibly and rapidlyforming a redox pair with a lithium ion during the charge and dischargecycles of a battery cell. An NGP is a single-layer graphene sheet or astack of several graphene sheets with each sheet being a hexagonalstructure of carbon atoms (single layer being as thin as 0.34 nm). Inthese two patent applications, the functionalized disordered carbon orNGP is used in the cathode (not the anode) of the lithium super-battery.In this cathode, lithium ions in the liquid electrolyte only have tomigrate to the edges or surfaces of graphene sheets (in the case offunctionalized NGP cathode), or the edges/surfaces of the aromatic ringstructures (small graphene sheets) in a disordered carbon matrix. Nosolid-state diffusion is required at the cathode. The presence of afunctionalized graphene or carbon enables reversible storage of lithiumon the surfaces (including edges), not the bulk, of the cathodematerial. Such a cathode material provides one type of lithium-storingor lithium-capturing surface. Typically, this surface has a functionalgroup thereon capable of forming a redox pair with a lithium ion.Another type of lithium-storing surface is based on simple lithiumdeposition on a surface of a nanostructured functional material.

In conventional lithium-ion batteries, lithium ions must diffuse intothe bulk of a cathode active material during discharge and out of thebulk of the cathode active material during re-charge. In theseconventional lithium-ion batteries, lithium ions must also diffuse inand out of the inter-planar spaces in a graphite crystal serving as ananode active material. The lithium insertion or extraction procedures atboth the cathode and the anode are very slow. Due to these slowsolid-state diffusion processes of lithium in and out of theseintercalation compounds, the conventional lithium ion batteries do notexhibit a high power density and the batteries require a long re-chargetime. None of these conventional devices rely on select functionalgroups (e.g. attached at the edge or basal plane surfaces of a graphenesheet) that readily and reversibly form a redox reaction with a lithiumion from a lithium-containing electrolyte.

In contrast, the lithium super-battery as reported in our two earlierpatent applications relies on the operation of a fast and reversiblereaction between a functional group (attached or bonded to a graphenestructure at the cathode) and a lithium ion in the electrolyte. Lithiumions coming from the anode side through a separator only have todiffuse, in the liquid electrolyte, to reach a surface/edge of agraphene plane at the cathode. These lithium ions do not need to diffuseinto or out of the interior of a solid particle. Since nodiffusion-limited intercalation is involved at the cathode, this processis fast and can occur in seconds. Hence, this is a totally new class ofhybrid supercapacitor-battery that exhibits unparalleled andunprecedented combined performance of an exceptional power density, highenergy density, long and stable cycle life, and wide operatingtemperature range. This device has the best of both battery andsupercapacitor worlds.

In the lithium super-batteries described in these two patentapplications, the anode comprises either particles of a lithiumtitanate-type anode active material (still requiring solid statediffusion at the anode), as schematically illustrated in FIG. 1(B), or alithium foil alone (without a nanostructured material to support orcapture the returning lithium ions/atoms during recharge), asillustrated in FIG. 1(C). In the latter case, lithium has to depositonto the front surface of an anode current collector alone (e.g. copperfoil) when the battery is recharged.

Since the specific surface area of a current collector is very low(typically <<1 m²/gram), the over-all lithium re-deposition rate isrelatively low and this process still can become surface area-limited.

Fully Surface-Controlled (Surface-Enabled), Lithium Ion-ExchangingBattery Device

Another superior energy storage device that also operates on lithium ionexchange between the cathode and the anode was reported in a co-pendingpatent application of ours [A. Zhamu, et al., “Surface-Controlled,Lithium Ion-Exchanging Energy Storage Device,” US Patent Publication No.US20120164539A1, filed Dec. 23, 2010.] In this new device, both thecathode and the anode (not just the cathode) have a lithium-capturing orlithium-storing surface (typically both being nanostructured with manylithium-storing surfaces) and both electrodes (not just the cathode)obviate the need to engage in solid-state diffusion. Both the anode andthe cathode have large amounts of surface areas to allow lithium ions todeposit thereon simultaneously, enabling dramatically higher charge anddischarge rates and higher power densities. The uniform dispersion ofthese surfaces of a nanostructured material (e.g. graphene, CNT,disordered carbon, nanowire, and nanofiber) in an electrode alsoprovides a more uniform electric field in the electrode in which lithiumcan more uniformly deposit without forming a dendrite. Such ananostructure eliminates the potential formation of dendrites, which wasthe most serious problem in conventional lithium metal batteries(commonly used in 1980s and early 1990s before being replaced bylithium-ion batteries). Such a device is herein referred to as a fullysurface-controlled (or surface-enabled), lithium ion-exchanging battery.

Sodium Ion Batteries and Sodium Compound-Based Supercapacitors

Aqueous electrolyte-based asymmetric or hybrid supercapacitors with asodium ion intercalation compound (NaMnO₂) as the cathode and activatedcarbon as the anode were investigated by Qu, et al [Q. T. Qu, Y. Shi, S.Tian, Y. H. Chen, Y. P. Wu, R. Holze, Journal of Power Sources, 194(2009) 1222]. Similar compounds (sodium birnessite, Na_(x)MnO₂) wereused as the electrode materials of another supercapacitor [L. Athouel,F. Moser, R. Dugas, O. Crosnier, D. Belanger, T. Brousse, Journal ofPhysical Chemistry C 112 (2008) 7270]. At least the cathode in thesesupercapacitors involves solid state diffusion (intercalation anddeintercalation) of Na ions in a Na_(x)MnO₂ solid. Furthermore, thesesupercapacitors do not involve exchange of Na ions between the anode andthe cathode. They still exhibit relatively low energy densities.

Sodium ion batteries using a hard carbon-based anode (Na-carbonintercalation compound) and a sodium transition metal phosphate as acathode have been described by several research groups: Zhuo, X. Y.Wang, A. P. Tang, Z. M. Liu, S. Gamboa, P. J. Sebastian, Journal ofPower Sources 160 (2006) 698; J. Barker, Y. Saidi, J. Swoyer, US PatentApplication US2005/0238961, 2005; J. Barker; M. Y. Saidi, and J. Swoyer,“Sodium Ion Batteries,” U.S. Pat. No. 7,759,008 (Jul. 20, 2010 and J. F.Whitacre, A. Tevar, and S. Sharma, “Na₄Mn₉O₁₈ as a positive electrodematerial for an aqueous electrolyte sodium-ion energy storage device,”Electrochemistry Communications 12 (2010) 463-466.

However, these sodium-based devices exhibit even lower specific energiesand rate capabilities than Li-ion batteries. These conventionalsodium-ion batteries require lithium ions to diffuse in and out of asodium intercalation compound at both the anode and the cathode. Therequired solid-state diffusion processes for sodium ions in a sodium-ionbattery are even slower than the Li diffusion processes in a Li-ionbattery, leading to excessively low power densities.

Partially and Fully Surface-Enabled, Metal Ion-Exchanging BatteryDevices (not Including Li Ions Alone)

Parallel to our work on the development of surface-controlled lithiumion-exchanging battery devices and lithium super-batteries, we have alsoconducted diligent research and development on batteries based on theexchange of other types of alkali ions than lithium, and other types ofmetal ions (such as alkaline-earth metals, transition metals,non-transition metals, such as aluminum, tin, and gallium, etc.). Noprior art had anticipated that these non-lithium ions, having vastlydifferent ionic sizes and electron affinity, electronegativity,electrochemical potential, or valency than lithium, could form a redoxreaction or chemical complex with any functional group at the cathode orat both the cathode and the anode material. Specifically, no prior arthad taught about or suggested that a divalent ion (e.g. Ca⁺²) ortrivalent ion (e.g. Al⁺³) could rapidly and reversibly form a redox pairor chemical complex with a surface-borne functional group, such ascarbonyl (>═O), on a surface (or edge) of a nanostructured material(e.g., NGP, CNT, or porous disordered carbon) for a battery application.No one had indicated that large ions like Na⁺, K⁺, Ca⁺², Zn⁺², and Al⁺³(all larger than Li⁺ ions) could be exchanged between the anode and thecathode in a fast and reversible manner, with or without intercalation.There had been no previous scientific basis to predict if asuper-battery or surface-enabled battery device could be based on thesenon-lithium ions. Our extensive and in-depth research has led to verysurprising, ground-breaking results that are herein reported.

The present invention provides partially or fully surface-enabled, metalion-exchanging battery devices, based on non-lithium metals such asnon-lithium alkali metals (Na, K, Rb, Cs, and Fr), alkaline metals(e.g., Be, Mg, Ca, and Ba), transition metals (e.g., Ti, V, Cr, Mn, Fe,Co, Ni, and Zn), and other metals (e.g. Al, Sn, Pb, etc). The instantapplication claims surface-enabled battery devices based on non-lithiumalkali metal ions (Na, K, Rb, Cs, Fr, and combinations thereof) andtheir mixtures with Li (but not Li alone). This application also claimssurface-enabled battery devices based on alkaline-earth metal ions,transition metal ions, and other types of metal ions that have asuitable electrochemical potential (e.g., not more than 3.0 volts lowerthan the reference Li/Li⁺ potential).

SUMMARY OF THE INVENTION

The present invention provides a partially or fully surface-controlled(surface-enabled), metal ion exchanging battery device. Using an alkaliion-exchanging battery device as an example, the alkali ion is selectedfrom sodium (Na), potassium (K), rubidium (Rb), caesium (Cs), francium(Fr), a combination thereof, or a combination of Na and/or K withlithium (Li), but not Li alone. The battery device comprises: (a) apositive electrode (cathode), (b) a negative electrode (anode), (c) aporous separator disposed between the two electrodes, and (d) a metalion-containing electrolyte in physical contact with the two electrodes,wherein at least one of the two electrodes contains therein a metal ionsource prior to the first charge or the first discharge cycle of thebattery device and at least the cathode (preferably both) of the twoelectrodes comprises a first functional or nanostructured materialhaving a metal ion-capturing or metal ion-storing surface. The operationof this device involves no metal ion intercalation in at least thecathode, and preferably in both of the two electrodes.

Additionally, the operation of this device does not involve theformation of a metal oxide (in contrast to that of a metal-air cell) ora metal sulfide (in contrast to that of a lithium-sulfur cell). Ingeneral, the operation of this battery device does not involve theintroduction of oxygen from outside the device and does not involve theformation of a metal oxide, metal sulfide, metal selenide, metaltelluride, metal hydroxide, or metal-halogen compound (e.g., metalchloride, metal iodide, etc). This new generation of energy storagedevice exhibits a dramatically higher energy density and significantlyhigher power density than those of conventional supercapacitors, and adramatically higher power density than that of the conventionallithium-ion battery. Both metal-air and lithium-sulfur cells exhibitstrong chemical reactions that are not surface-enabled. They arechemical reaction-limited, extremely slow, and exhibiting powerdensities even lower than those of conventional lithium-ion cells.

The metal ion is selected from the following groups of metals: (A)alkali metal including sodium (Na), potassium (K), rubidium (Rb),caesium (Cs), francium (Fr), or a combination thereof; (B)alkaline-earth metal including beryllium (Be), magnesium (Mg), calcium(Ca), strontium (Sr), barium (Ba), radium (Ra), or a combinationthereof; (C) transition metals; (D) other metals selected from aluminum(Al), gallium (Ga), indium (In), tin (Sn), lead (Pb), or bismuth (Bi);or (E) a combination thereof. The transition metal is preferablyselected from scandium (Sc), titanium (Ti), vanadium (V), chromium (Cr),manganese (Mn), iron (Fe), cobalt (Co), nickel (Ni), zinc (Zn), cadmium(Cd), or a combination thereof. These metal elements have a negativeelectrochemical potential relative to hydrogen, and the difference inelectrochemical potential between any of these metals and lithium is nogreater than 3.0 volts.

For the purpose of defining the scope of the claims in this patentapplication, the term “metal ion-exchanging” means that the discharge ofthe battery device involves metal ions migrating from one electrode(e.g., anode) to the other electrode (e.g. cathode) and that therecharge of the battery device involves metal ions migrating in thereverse direction (e.g., from the cathode to the anode). Theconventional supercapacitors (both symmetric and asymmetric) do not meetthis requirement since no ion exchange occurs between the twoelectrodes.

The term “surface-controlled” or “surface-enabled” means that theinteraction between metal ions and an electrode (the capturing orstoring of metal ions by an electrode) are essentially limited tosurfaces of the electrode, involving no solid state diffusion of metalions in and out of the bulk of a solid electrode active material (i.e.not requiring intercalation). The interaction is also not limited by theexcessively low surface area of an electrode; i.e. not surfacearea-limited. Conventional lithium-ion, sodium-ion, and potassium-ionbatteries do not meet this definition. If only one of the two electrodes(i.e., the cathode) of a battery cell is surface-enabled and also notsurface area-limited, the battery device is said to be a partiallysurface-controlled (partially surface-enabled) device. If bothelectrodes are surface-enabled and not surface area-limited, the batterydevice is said to be fully surface-enabled.

For the purpose of further defining the claims in the instantapplication, the presently claimed surface-enabled or surface-mediatedbattery device does not include metal-air or metal-oxygen cells whereinthe cathode reactions during cell discharge involve a strong reaction ofmetal ions with oxygen molecules introduced from outside the batterycell, resulting in the formation of a metal oxide (such as Li₂O, Al₂O₃,and ZnO). In a metal-air cell, the cathode active material (oxygen) isnot part of the battery cell. This reaction between metal ions andoxygen is not electrode surface-enabled (i.e. not mediated or enabled bya surface of a cathode active material). This reaction is alsoessentially irreversible without the assistance of a catalyst and, evenwith a catalyst, the reversible reaction (re-charging operation) isextremely slow, even slower than that of a conventional lithium-ionbattery. Additionally, the operation of the presently inventedsurface-enabled battery device does not involve melting of an electrodeactive material (e.g. does not involve melting of sodium or potassiummetal), does not use an electro-catalyst (e.g. to catalyze the anode orcathode reaction), does not involve the formation of a metal oxidespecies, and does not involve the formation of a metal sulfide (e.g.Li_(x)S).

As examples, the presently invented device includes either a partiallyor a fully surface-controlled (surface-enabled), alkali ion-exchangingbattery device. In this instant invention, the alkali ion is selectedfrom sodium (Na), potassium (K), rubidium (Rb), caesium (Cs), francium(Fr), or a combination thereof. By contrast, in earlier applications aslisted above, lithium ions are the only type of ions being exchangedbetween an anode and a cathode.

The electrolyte preferably comprises liquid electrolyte or gelelectrolyte (including polymer electrolyte) in which metal ions have ahigh diffusion coefficient. Solid electrolyte is normally not desirable,but some thin layer of solid electrolyte may be used if it exhibits arelatively high diffusion coefficient. The electrolyte preferablycomprises an organic electrolyte (e.g. sodium salt dissolved in anorganic solvent) or ionic liquid (e.g., sodium-doped ionic liquid).Aqueous electrolyte can be used if the alkali metal source does notcontain non-ionized alkali metal. It may be noted that the electrolytein a surface-enabled device containing a source of a first metal cancontain an ion of a second metal different than the first metal. Inother words, as examples, a sodium-exchanging battery can have anelectrolyte containing ions of lithium, potassium, calcium, zinc, or acombination thereof as a major or minor type of ion being exchangedbetween an anode and a cathode.

For convenience, sodium (Na) ion is used as a primary type of ions beingexchanged between an anode and a cathode, but this is used as an exampleonly and the instant application is not limited to Na ion-based energystorage devices.

A partially surface-enabled, metal ion-exchanging battery is basically ametal ion-based super-battery. Two examples of such a super-battery aregiven in FIG. 1(B) and FIG. 1(C). This device is composed of a positiveelectrode (cathode), a negative electrode (anode), a porous separatordisposed between the two electrodes, and a metal ion-containingelectrolyte (e.g., sodium ion-based electrolyte) in physical contactwith the two electrodes. An electrolyte component, not shown in FIG.1(B) and FIG. 1(C), permeates into the anode, cathode, and the pores ofthe separator. A particularly important feature of the positiveelectrode is that it preferably comprises a nanostructured functionalmaterial (e.g. a chemically functionalized, nanostructured disorderedcarbon, nanographene, or carbon nanotube) having a surface-bornefunctional group that is capable of reversibly reacting with a metalatom or ion, forming a redox pair with a metal atom/ion or forming achemical complex with a metal atom/ion during the charge and dischargecycles. The surface-borne functional group is at the edge or on thesurface of a nanostructured material (e.g., at an edge or on a surfaceof a graphene sheet). Although there is no limitation on the electrodethickness, the presently invented positive electrode preferably has athickness greater than 10 μm, more preferably greater than 50 μm, andmost preferably greater than 100 μm.

As illustrated in FIG. 1(C), FIG. 2(A), FIG. 2(B), and FIG. 2(C), andusing sodium ion as an example for the type of ions being exchangedbetween an anode and a cathode, when a super-battery is made (prior tothe first discharge cycle, as shown in FIG. 2(A)), a sodium source(e.g., powder or foil of sodium) is implemented between an anode currentcollector and a separator. During the first discharge, sodium foil orpowder is ionized to supply sodium ions that go into the electrolyte(electrolyte being preferably in a liquid or gel state). These ionsmigrate from the anode, through the separator pores, into the cathodeside. This process involves only liquid-state diffusion and, hence, isfast. These ions are captured by functional groups on the surfaces(including edges) of a functional material (preferably a nanostructuredmaterial) at the cathode. Capturing of metal ions means allowing themetal ions to reversibly react with a surface functional group (e.g.,forming a redox pair with this group or forming a chemical complex withthis group), or simply adsorb or deposit onto a surface of thisfunctional or nanostructured material. This would obviate the need formetal ions to enter the bulk of a cathode active material (such a slowsolid-state diffusion is required of a conventional alkali ion battery).FIG. 2(B) schematically shows that a majority or all of the sodium ionshave been captured on the surfaces at the cathode.

During the subsequent re-charge operation, metal ions (sodium ions inthis example) are released from the surfaces of a functional material atthe cathode, migrate through the separator pores into the anode zonewhere no anode active material or functional material exists, only acurrent collector (FIG. 2(C)). These sodium ions are deposited onto asurface of the current collector. As will be further discussed later, acurrent collector has a limited surface area (typically <<1 m²/g), whichmay or may not be able to simultaneously accommodate large amounts ofalkali ions swarming back from the cathode into the anode all at thesame time, particularly in a high current density situation. There-charge process could become surface area-limited at the anode.

Another partially surface-enabled, alkali ion-exchanging battery (oralkali super-battery) is schematically shown in FIG. 1(B) or FIG. 3(A)and FIG. 3(B). In this device, an alkali ion source is implemented inthe anode zone, which is an alkali-containing compound, such asNa₄Mn₉O₁₈ and NaV_(1-x)Cr_(x)PO₄F, which are commonly used as a cathodeactive material (not anode) in a conventional sodium-ion battery. It maybe noted that non-porous, typically micron-scaled hard carbon particlesare used as the anode active material and either Na₄Mn₉O₁₈ [Whitacre, etal] or NaV_(1-x)Cr_(x)PO₄F [Zhuo, et al] is used as the cathode activematerial in conventional Na-ion batteries. In contrast, Na₄Mn₉O₁₈ orNaV_(1-x)Cr_(x)PO₄F, is used as a sodium source at the anode of thepartially surface-enabled battery. Many other types of sodium-containingcompound (e.g. Na_(x)Ti₂O₄) may be used as a sodium source. In addition,we have also surprisingly observed that conjugated alkali dicarboxylate(e.g., disodium terephthalate, Na₂C₈H₄O₄, or di-potassium terephthalate,K₂C₈H₄O₄) and alkali rhodizonate (e.g. Na_(x)C₆O₆, x=2-6) can also beused as an alkali source in the presently invented alkali super-batteryor partially surface-enabled battery.

As illustrated in FIG. 3(A) and FIG. 3(B), when the battery device isdischarged, the alkali-containing material at the anode releases alkaliions (e.g. Na⁺ or K⁺), which migrate (in liquid electrolyte) throughseparator pores into the cathode zone. These ions are captured at or bythe functional surfaces at the cathode and there is no need to undergosolid-state diffusion at the cathode side. When the battery isre-charged, alkali ions are released from the functional surfaces at thecathode and migrate back to the anode side. However, these ions mustre-enter the interior of their parent compounds. This could involve somesolid-state diffusion at the anode and, hence, this device is referredto as a partially surface-enabled device (only the cathode side issurface-enabled). Again, alkali ions are used as examples of metal ions.The approach herein discussed is not limited to alkali metals.

To illustrate the operational principle of a fully surface-enabled,alkali ion-exchanging battery device (FIG. 4(A)), one may consider acase wherein an alkali source (e.g. small pieces of sodium foil orpowder) is implemented between a nanostructured anode (e.g. composed offunctionalized graphene sheets) and a porous polymer separator when thebattery device is made, and wherein a nanostructured cathode comprisesfunctionalized graphene sheets surrounded by interconnected pores thatare preferably mesoscaled (2 nm-50 nm), but can be smaller than 2 nm.Referring to FIG. 4(A) to FIG. 4(C), during the first discharge cycle,alkali foil is ionized to generate alkali ions in the liquidelectrolyte. Alkali ions rapidly migrate through the pores of thepolymer separator into the cathode side. Since the cathode is alsomesoporous having interconnected pores to accommodate liquid electrolytetherein, alkali ions basically just have to sail through liquid to reacha functional group on a surface or edge of a graphene sheet at thecathode. The subsequent surface redox reaction between an alkali ion anda surface-borne functional group (e.g., carbonyl, >C═O illustrated inFIG. 5(C)) is fast and reversible. Because all the steps (alkaliionization, liquid phase diffusion, and surface redox reaction) are fastand no solid-state diffusion is required, the whole process is veryfast, enabling fast discharging and a high power density. This is instark contrast to the conventional lithium-ion battery or sodium-ionbattery wherein lithium or sodium ions are required to diffuse into thebulk of a solid cathode particle (e.g., micron-sized lithium cobaltoxide or Na₄Mn₉O₁₈ particles at the cathode), which is a very slowprocess.

In the above example, the discharge process continues until either thealkali foil or powder (an example of a metal ion source) is completelyionized or all the functional groups at the cathode side are exhausted(i.e. each and every group has captured an alkali ion). Duringre-charge, alkali ions are released from the surface functional groupsat the cathode, diffuse through liquid electrolyte, and get captured bysurface-borne functional groups at the anode side (or simply getdeposited onto a surface of the nanostructured anode material). Again,no solid-state diffusion is required and, hence, the whole process isvery fast, requiring a short re-charge time. This is as opposed to therequired solid-state diffusion of lithium ions (or sodium ions) into thebulk of graphite particles at the anode of a conventional lithium-ionbattery (or a conventional sodium-ion battery). The nanostructured anodehaving a high specific surface area also provides sufficient surfaces toreceive large amounts of alkali ions swarming back from the cathode,enabling simultaneous deposition or capturing of a large flux of ions.Such a nanostructured anode will not be surface area-limited, as opposedto the situation in FIG. 2(C), where only a current collector exists (nonanostructured material at the anode).

Clearly, this battery device provides a very unique platform ofexchanging metal ions between an anode and a cathode that requires nosolid-state diffusion or intercalation in both electrodes. The processis substantially dictated by the surface reactions (surface ionization,surface deposition, or surface redox reaction), plus the liquid-phasediffusion (all being very fast). Hence, the device is herein referred toas a surface-controlled (or, preferably, surface-enabled orsurface-mediated), metal ion-exchanging battery. This is a totallydifferent and patently distinct class of energy storage device than theconventional lithium-ion or sodium-ion battery, wherein solid-statediffusion or intercalation is required at both the anode and the cathodeduring both the charge and discharge cycles.

This new surface-enabled, metal ion-exchanging battery device is alsopatently distinct from the conventional supercapacitor that operates onthe electric double layer (EDL) mechanism or pseudo-capacitancemechanism. In both mechanisms, no metal ions are exchanged between thetwo electrodes. In particular, our new battery device is patentlydistinct from the LBL CNT-based symmetric supercapacitor of Lee, et al[Nature Nanotechnology, 5 (2010) 531-537], wherein both the anode andthe cathode are ultra-thin CNT structures prepared by the layer-by-layer(LBL) process. This symmetric supercapacitor does not contain an extraalkali source and does not involve exchange of alkali ions between twoelectrodes. Furthermore, in the report of Lee, et al, the super-batterydevice containing a lithium foil as the anode does not contain ananostructured functional material at the anode (as schematicallyillustrated in FIG. 1(C)). The anode only has a current collector onwhich the returning lithium ions are deposited during re-charge. This isa surface area-limited case. Lee, et al also discloses a super-batteryconsisting of a lithium titanate anode (not a source of non-lithiumalkali ions) and a LBL CNT cathode.

The presently invented surface-enabled, metal ion-exchanging device(including the alkali ion-exchanging battery device) is also patentlydistinct from the lithium super-battery as disclosed in two of ourearlier applications, which do not have a functional material at theanode. The anode side only contains an anode current collector. In thepresently invented fully surface-enabled battery device, not only thecathode but also the anode has large amounts of surface areas to allowmetal ions to deposit thereon simultaneously, enabling dramaticallyhigher charge and discharge rates and higher power densities. In otherwords, in a high current density situation (during fast re-charging),great amounts of metal ions swarm into the anode side, each looking fora site to deposit or react onto. The anode current collector alone hasonly a small amount of surface area available at one time, incapable ofaccommodating such a high flux of metal ions. By contrast, the hugespecific surface area of a nanostructured functional material (e.g.,graphene or CNT) is capable of accommodating a huge amount of alkaliions at the same time.

In addition, the uniform dispersion of these surfaces of a nanomaterial(e.g. graphene or CNT) in an electrode also provides a more uniformelectric field in the electrode in which metal ions/atoms can moreuniformly deposit without forming a dendrite. More surface areas alsomean more deposition spots and each spot only has a small quantity ofmetal atoms, insufficient to form a dangerous dendrite. Such ananostructure eliminates the potential formation of dendrites, which wasthe most serious problem in conventional lithium metal batteries.

In this device, preferably at least one of the two electrodes has afunctional material having a functional group (e.g., carbonyl) that iscapable of reversibly reacting with a metal atom or ion. Preferably,both of the two electrodes have a functional material having afunctional group that reversibly reacts or interacts with a metal atomor ion (e.g. to form a surface redox pair or a chemical complex).Preferably, at least one of the two electrodes has a nanostructuredfunctional material having a high specific surface area no less than 10m²/gram (preferably >100 m²/gram, more preferably >500 m²/gram, furtherpreferably >1,000 m²/gram, and most preferably >1,500 m²/gram) to storeor support metal ions or atoms thereon. More preferably, both electrodeshave a nanostructured functional material having a high specific surfacearea no less than 10 m²/gram (preferably >100 m²/g, more preferably >500m²/gram, further preferably >1,000 m²/gram, and most preferably >1,500m²/gram) to store or support metal ions or atoms thereon.

Preferably, the alkali source (as an example of a metal ion source)comprises an alkali metal chip, alkali metal foil, alkali powder,surface-passivated or stabilized alkali metal or metal alloy particles,or a combination thereof. The alkali ion source may be implemented atthe anode side before the first discharge procedure is carried out onthis battery device. Alternatively, the alkali source may be implementedat the cathode side before the first charge procedure is carried out onthis battery device. As another alternative, both the cathode and theanode may be fabricated to contain some alkali ion source during thebattery manufacturing process. It is important to note that this solidalkali source provides the majority of the alkali ions that are to beexchanged between the anode and the cathode during the charge-dischargecycles. Although the alkali ion-containing electrolyte naturallyprovides some of the needed alkali ions, this amount is way too short toenable the battery device to deliver either a high energy density or ahigh power density. This is why the symmetric supercapacitor of Lee etal (with both the anode and the cathode containing only LBL CNTs, but noadditional solid lithium source) performs so poorly in terms of both theenergy density and power density [Lee, et al, Nature Nanotechnology, 5(2010) 531-537]. These were simply no lithium or other alkali ions beingexchanged between the cathode side and the anode side.

In the presently invented battery device, at least a functional material(preferably all the functional materials in both electrodes) is (are)selected from the group consisting of:

-   (a) a nanostructured or porous disordered carbon material selected    from a soft carbon, hard carbon, polymeric carbon or carbonized    resin, mesophase carbon, coke, carbonized pitch, carbon black,    activated carbon, or partially graphitized carbon;-   (b) a nanographene platelet selected from a single-layer graphene    sheet or multi-layer graphene platelet;-   (c) a carbon nanotube selected from a single-walled carbon nanotube    or multi-walled carbon nanotube;-   (d) a carbon nanofiber, nanowire, metal oxide nanowire or fiber,    conductive polymer nanofiber, or a combination thereof.-   (e) a carbonyl-containing organic or polymeric molecule;-   (f) a functional material containing a carbonyl, carboxylic, or    amine group; and-   (g) combinations thereof.

Although CNTs are not particularly desired nanostructured materials dueto the high costs and other technical issues, CNTs (alone or incombination with other functional or nanostructured material) can stillbe used in the presently invented surface-controlled alkaliion-exchanging battery.

The functional material in the anode and/or cathode may be selected fromthe group consisting ofpoly(2,5-dihydroxy-1,4-benzoquinone-3,6-methylene) (PDBM), M_(x)C₆O₆(x=1-3), M₂(C₆H₂O₄), M₂C₈H₄O₄ (alkali metal terephthalate), M₂C₆H₄O₄(alkali metal trans-trans-muconate),3,4,9,10-perylenetetracarboxylicacid-dianhydride (PTCDA) sulfidepolymer, PTCDA, 1,4,5,8-naphthalene-tetracarboxylicacid-dianhydride(NTCDA), benzene-1,2,4,5-tetracarboxylic dianhydride,1,4,5,8-tetrahydroxy anthraquinon, tetrahydroxy-p-benzoquinone, andcombinations thereof, where M is an alkali metal element. These organicor polymeric materials (molecules or salts) possess functional groups(e.g. carbonyl group) capable of undergoing a reversible and fast redoxreaction with an alkali ion or atom. These functional materials tend tohave a relatively low electronic conductivity and, hence, preferably thefunctional material selected from this group is combined with (e.g.chemically bonded or attached to a nanostructured material, such asnanographene, carbon nanotube, disordered carbon, nanographite, materialselected from nanographene, carbon nanotube, disordered carbon,nanographite, metal nanowire, conductive nanowire, carbon nanofiber, andpolymeric nanofiber). For instance, both graphene and the constituentaromatic rings of a disordered carbon (soft carbon, hard carbon,activated carbon, carbon black, etc) can have, on their edges orsurfaces, functional groups that can react with the matting functionalgroups on the aforementioned functional materials (e.g. the hydroxylgroup on tetrahydroxy-p-benzoquinone).

Alternatively, a nanostructured carbon material, such asnon-functionalized nanographene, carbon nanotube, porous disorderedcarbon, or nanographite, may simply provide a surface upon which lithiumatoms can be deposited, e.g. via electrochemical deposition.Non-functionalized surface can still serve as a physical support orsubstrate for alkali atoms. The mere existence of a nanostructuredmaterial, even without a reactive functional group, can still provide ahuge amount of supporting surfaces. This non-functionalized surface isthe second type of alkali-storing surface in the present context.

The disordered carbon material may be formed of two phases with a firstphase being small graphite crystals or stacks of graphene planes and asecond phase being non-crystalline carbon and wherein the first phase isdispersed in the second phase or bonded by the second phase. Thedisordered carbon material may contain less than 90% by volume ofgraphite crystals and at least 10% by volume of non-crystalline carbon.

The functional materials may comprise nanographene selected from asingle-layer graphene sheet or a multi-layer graphene platelet.Alternatively, the functional materials may comprise single-walled ormulti-walled carbon nanotube. In the battery device, at least one of thefunctional materials is a nanostructured material having a specificsurface area of at least 100 m²/g, preferably at least 500 m²/g, andmore preferably at least 1,000 m²/g, and most preferably at least 1,500m²/g.

Preferably, at least one of the functional materials has a functionalgroup selected from the group consisting of —COOH, ═O, —NH₂, —OR, and—COOR, where R is a hydrocarbon radical.

The alkali ion source may be selected from alkali metal (e.g., in a thinfoil or powder form, preferably stabilized or surface-passivated), analkali metal alloy, a mixture of alkali metal or alkali alloy with analkali intercalation compound, an alkali-bearing compound, alkalititanium dioxide, alkali titanate, alkali manganate, analkali-transition metal oxide, Na_(x)Ti_(y)O_(z), or a combinationthereof. Specifically, the alkali intercalation compound oralkali-bearing compound may be selected from the following groups ofmaterials:

-   (a) alkali alloyed or intercalated silicon (Si), germanium (Ge), tin    (Sn), lead (Pb), antimony (Sb), bismuth (Bi), zinc (Zn), aluminum    (Al), titanium (Ti), cobalt (Co), nickel (Ni), manganese (Mn),    cadmium (Cd), and mixtures thereof;-   (b) alkali-doped or alkali-intercalated intermetallic compounds of    Si, Ge, Sn, Pb, Sb, Bi, Zn, Al, Ti, Co, Ni, Mn, Cd, and their    mixtures;-   (c) alkali-doped or alkali-intercalated oxides, carbides, nitrides,    sulfides, phosphides, selenides, tellurides, or antimonides of Si,    Ge, Sn, Pb, Sb, Bi, Zn, Al, Fe, Ti, Co, Ni, Mn, Cd, and mixtures or    composites thereof, and-   (d) alkali salts.

The electrolyte may be selected from any of the electrolytes used inconventional sodium-ion batteries or alkali ion-containing saltsdissolved in a solvent. The electrolyte may comprise an alkalisalt-doped ionic liquid. In the battery device, the positive electrodepreferably has a thickness greater than 5 μm, preferably greater than 50μm, and more preferably greater than 100 μm.

Quite surprisingly, the battery device provides an energy density thatis typically no less than 100 Wh/kg, but can reach >500 Wh/kg (based onthe electrode weight). This is significantly higher than the energydensity (25 Wh/kg based on an electrode weight, or 5 Wh/kg based on thecell weight) of conventional supercapacitors. The power density canreach a level >>100 Kw/kg, also based on an electrode weight. Moretypically, the battery device provides an energy density greater than200 Wh/kg and power density greater than 50 Kw/kg. In many cases, thebattery device provides an energy density greater than 300 Wh/kg. Insome cases, the power density is significantly higher than 100 Kw/kg, oreven higher than 200 Kw/kg, which is orders of magnitude higher than thepower densities (0.5 Kw/kg) of conventional lithium-ion batteries and iseven significantly higher than those (1-10 Kw/kg) of conventionalsupercapacitors.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1(A) a prior art lithium-ion battery or sodium-ion cell usinggraphite or hard carbon as an anode active material and lithium ironphosphate or sodium manganese oxide (Na₄Mn₉O₁₈) as a cathode activematerial;

FIG. 1(B) an alkali super-battery cell (partially surface-enabledbattery) with a sodium manganese oxide (Na₄Mn₉O₁₈) as an anode activematerial and a cathode made of a functional material (e.g.,functionalized nanographene, CNT, or disordered carbon powder);

FIG. 1(C) another type of alkali super-battery cell with an anode ofalkali foil or powder (but no nanostructured functional material) and acathode made of functionalized graphene, CNT, or disordered carbon;

FIG. 1(D) an example of the fully surface-enabled, alkali ion-exchangingbattery device, which contains a nanostructured functional material(with or without a functional group capable of reacting with alkali ionsor atoms) at the anode, an alkali source (e.g. alkali foil orsurface-passivated alkali powder), a porous separator, liquid or gelelectrolyte (liquid being preferred), a nanostructured functionalmaterial at the cathode.

FIG. 2(A) The structure of a partially surface-enabled, alkaliion-exchanging battery device when it is made (prior to the firstdischarge or charge cycle), containing an anode current collector (butno nanostructured functional material) at the anode side, an alkalisource (e.g. alkali foil or surface-stabilized alkali powder), a porousseparator, liquid electrolyte, a nanostructured functional material atthe cathode;

FIG. 2(B) The structure of this battery device after its first dischargeoperation (alkali is ionized with the alkali ions diffusing throughliquid electrolyte to reach surface-borne functional groups in thenanostructured cathode and rapidly react with these groups);

FIG. 2(C) The structure of this battery device after being re-charged(alkali ions are released from the cathode surface, diffusing throughliquid electrolyte to reach a surface of a current collector).

FIG. 3(A) The structure of another partially surface-enabled, alkaliion-exchanging battery device when it is made (prior to the firstdischarge or charge cycle), containing an anode current collector and analkali intercalation compound (as an alkali source) at the anode side, aporous separator, liquid electrolyte, a nanostructured functionalmaterial at the cathode;

FIG. 3(B) The structure of this battery device in a discharged statewhere alkali ions were released from the anode, diffusing through liquidelectrolyte to reach surface-borne functional groups in thenanostructured cathode and rapidly react with these groups.

FIG. 4(A) The structure of a fully surface-enabled, alkaliion-exchanging battery device when it is made (prior to the firstdischarge or charge cycle), containing an anode current collector and ananostructured functional material at the anode side, an alkali source(e.g. alkali foil or surface-stabilized alkali powder), a porousseparator, liquid electrolyte, a nanostructured functional material atthe cathode;

FIG. 4(B) The structure of this battery device after its first dischargeoperation (alkali is ionized with the alkali ions diffusing throughliquid electrolyte to reach surface-borne functional groups in thenanostructured cathode and rapidly react with these groups);

FIG. 4(C) The structure of this battery device after being re-charged(alkali ions are released from the cathode surface, diffusing throughliquid electrolyte to reach surface-borne functional groups in thenanostructured anode and rapidly react with these groups). If thenanostructured anode does not have functional groups to capture thereturning alkali ions, at least the huge surface areas can still serveas a supporting substrate onto which massive amounts of alkali ions canelectro-deposit concurrently. Such a massive, simultaneous depositioncannot be accomplished with the anode current collector alone whichtypically has a low specific surface area.

FIG. 5(A) Schematic of a typical structure of a disordered carbon (as anexample of a nanostructured functional material) that is highly porouswith pores accessible by liquid electrolyte in such a manner that thefunctional groups attached to an edge or surface of an aromatic ring orsmall graphene sheet can readily react with alkali ions;

FIG. 5(B) Examples of functional groups capable of reversibly reactingwith alkali ions. Alkali ions are not required to enter the interior ofa solid particle (no solid state diffusion is necessary), as opposed toa conventional lithium-ion battery wherein lithium ions must diffusethrough a narrow channel of a solid compound (e.g., a LiFePO₄ particle);and

FIG. 5(C) A possible alkali storage mechanism, which is fast,reversible, and stable.

FIG. 6(A) Schematic of a soft carbon, wherein neighboring stacks ofgraphene sheets or small aromatic rings are favorably oriented withrespect to each other at a small angle that is conducive to the growthor merging (graphitizable);

FIG. 6(B) Schematic of hard carbon (non-graphitizable);

FIG. 6(C) carbon black, having a large number of small aromatic ringdomains arranged to form a nanoscaled spherical particle; and

FIG. 6(D) an individual carbon black particle that has been activated toopen up small gates that enable liquid electrolyte to access the edge-or surface-borne functional groups inside a particle.

FIG. 7 SEM image of curved graphene sheets (curved NGPs).

FIG. 8(A) Estimated total diffusion times plotted as a function of theNa₄Mn₉O₁₈ particle size for a partially surface-enabled device (withNa₄Mn₉O₁₈ being implemented at the anode side as a sodium ion source andNGP as a nanostructured cathode) and a conventional sodium-ion battery(having non-porous hard carbon as the anode active material andNa₄Mn₉O₁₈ as the cathode active material); and

FIG. 8(B) Estimated total diffusion times plotted as a function of thenanostructured cathode thickness for another partially surface-enabledbattery device (Na Foil/f-CNT with a 20-μm foil zone and a 50-μmseparator).

FIG. 9(A) Estimated total diffusion times plotted as a function of thenanostructured electrode thickness for a fully surface-enabled cell(NGP-Na/f-NGP, 50-μm separator) and

FIG. 9(B) Those for a fully surface-enabled cell (10-μm separator).

FIG. 10 Ragone plot of a partially surface-enabled, potassiumion-exchanging battery having a functionalized disordered carbon-basedcathode and a K source at the anode (with an anode current collectoronly, no nanostructured anode material) and that of a correspondingfully surface-enabled, potassium ion-exchanging battery device (composedof a disordered carbon anode, a K ion source at the anode, and porous,functionalized disordered carbon cathode). As compared to a prior artLBL-CNT/LBL-CNT symmetric supercapacitor, both devices exhibitsignificantly higher energy densities.

FIG. 11 Ragone plot of four types of cells: a fully surface-enabledalkali ion-exchanging battery, a partially surface-enabledalkali-exchanging cell (containing Na metal powder or foil as a metalion source at the anode and a functionalized NGP cathode), anotherpartially surface-enabled alkali ion-exchanging battery (with ananostructured NaMnO₂ anode and functionalized NGP cathode), and a priorart asymmetric supercapacitor (Qu, et al) composed of a conventionalactivated carbon anode, NaMnO₂ cathode (micron-scaled particles), andaqueous Na₂SO₄ electrolyte.

FIG. 12(A) The carbonyl groups on PDBM cathode material is capable offorming redox pairs with sodium ions (not just lithium ions); and

FIG. 12(B) Ragone plot of a partially surface-enabled sodiumion-exchanging battery containing a carbonyl-containing organic material(bulk PDBM particles mixed with non-porous carbon black particles as aconductive additive) as the anode and nanostructured NGP as cathode, andthe Ragone plot of a corresponding fully surface-enabled battery with ananographene-supported PDBM anode and a functionalized nanographenecathode. The PDBM molecules are supported by (partially bonded to)graphene oxide surface.

FIG. 13 Ragone plots for three different surface-enabled metalion-exchanging batteries: Ca, Zn, and Al ion-based.

FIG. 14 Various plausible surface-mediated metal ion-storing orcapturing mechanisms: A. Prior art surface redox pair between a carbonylgroup and a lithium ion; B. surface redox pair between a carbonyl groupand a sodium ion; C. surface chemical complex between a carbonyl groupand a calcium ion; and D. surface chemical complex between a carbonylgroup and an aluminum ion.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The present invention may be understood more readily by reference to thefollowing detailed description of the invention taken in connection withthe accompanying drawing figures, which form a part of this disclosure.It is to be understood that this invention is not limited to thespecific devices, methods, conditions or parameters described and/orshown herein, and that the terminology used herein is for the purpose ofdescribing particular embodiments by way of example only and is notintended to be limiting the claimed invention.

This invention provides an electrochemical energy storage device that isherein referred to as a surface-enabled, metal ion-exchanging battery.This device exhibits a power density significantly higher than the powerdensities of conventional supercapacitors and dramatically higher thanthose of conventional lithium ion batteries. This device also exhibitsan energy density comparable to that of a battery, and significantlyhigher than those of conventional supercapacitors.

The present invention provides a partially or fully surface-enabled,metal ion-exchanging battery device. The fully surface-enabled,ion-exchanging battery is composed of a positive electrode containing afunctional material having a metal ion-storing or metal ion-capturingsurface (the functional material being preferably nanostructured withnanoscaled or meso-scaled pores), a negative electrode containing afunctional material having a metal ion-storing or metal ion-capturingsurface (preferably nanostructured with nanoscaled or mesoscaled pores),a porous separator disposed between the two electrodes, and a metalion-containing electrolyte in physical contact with the two electrodes.A particularly desirable feature of the negative electrode (anode)and/or the positive electrode (cathode) is that the electrode comprisesa chemically functionalized material (e.g., nanographene, carbonnanotube, porous disordered carbon particles, etc) having a functionalgroup that is capable of rapidly and reversibly reacting with a metalatom or ion during the charge and discharge cycles.

In a partially surface-enabled, alkali ion-exchanging battery device asan example (e.g. as illustrated in FIG. 1(C), FIG. 2(A), FIG. 2(B), andFIG. 2(C) the anode side contains an alkali ion source (e.g. foil orpowder of sodium or potassium) when the battery is made, but nonanostructured functional material (only a current collector exists toreceive the alkali ions returning from the cathode during a re-chargeoperation). All other features are similar to those in a fullysurface-enabled counterpart. In other words, the metal ion-exchangingbattery is composed of a positive electrode containing a functionalmaterial having an alkali ion-storing or alkali ion-capturing surface(the functional material being preferably nanostructured with nanoscaledor mesoscaled pores). In particular, the cathode comprises a chemicallyfunctionalized material (e.g., nanographene, carbon nanotube, porousdisordered carbon particles, etc) having a functional group that iscapable of rapidly and reversibly reacting with an alkali atom or ionresiding in electrolyte during the charge and discharge cycles.

In another partially surface-enabled battery device (e.g., asschematically illustrated in FIG. 1(B), FIG. 3(A), and FIG. 3(B), theanode comprises an alkali intercalation compound (e.g., Na₄Mn₉O₁₈,NaV_(1-x)Cr_(x)PO₄F, or Na_(x)Ti₂O₄, which are preferably in ananoparticle form). Alternatively, the anode may comprise an anodeactive material (e.g. un-treated solid hard carbon containing nomesopores) plus an alkali ion source, wherein the anode active materialrequires intercalation or solid state diffusion of alkali ions. In otherwords, the anode side is not surface-enabled, only the cathode side is.

Although there is no limitation on the electrode thickness, thepresently invented positive electrode preferably has a thickness greaterthan 5 μm, more preferably greater than 50 μm, and most preferablygreater than 100 μm.

Theoretical Aspects (Alkali Ion Diffusion Kinetics of ConventionalSodium-Ion Batteries and the New Surface-Enabled, Alkali Ion-ExchangingBattery Devices)

Not wishing to be constrained by any theory, but we would like to offerthe following theoretical considerations that perhaps are helpful to thereaders. We will provide some insight as to how partially and fullysurface-enabled alkali ion-exchanging battery devices operate, and whysuch batteries exhibit exceptional power densities un-matched byconventional lithium-ion and sodium-ion batteries. The power densitiesof these surface-enabled devices are even surprisingly higher than thoseof conventional supercapacitors. We will also shed some light on why theelectrode thickness of alkali batteries (including partially and fullysurface-enabled and conventional sodium-ion batteries) plays such acritical role in dictating the power density in such a dramatic manner.

The internal structure of a conventional sodium-ion battery may beschematically shown in FIG. 1(A). In a battery discharge situation,sodium ions must diffuse out of an anode active material particle, suchas non-porous hard carbon solid particles (particle diameter=d_(a) andthe average solid-state diffusion distance=d_(a)/2), and then diffuse inliquid electrolyte across the anode thickness (anode layer thickness=Laand the average diffusion distance=La/2). Subsequently, sodium ions mustmove (in liquid electrolyte) across a porous separator (thickness=Ls),diffuse across part of the cathode thickness (thickness=Lc) in liquidelectrolyte to reach a particular cathode active material particle(average diffusion distance=Lc/2), and then diffuse into the bulk of aparticle (diameter=d_(c) and the average solid-state diffusion distancerequired=d_(c)/2). In a re-charge situation, the sodium ions move in theopposite direction, but must travel approximately the same distances. Itmay be noted that, in general, diffusion through a liquid is fast anddiffusion through a solid is slow. The differences in diffusion ratesare one important factor that differentiates the new battery device fromthe conventional sodium ion battery.

Assume that the diffusion coefficient of sodium ions in a particularmedium is D and a required travel distance is x, then the requireddiffusion time will be t˜x²/D, according to a well-known kineticsequation. As a first-order of approximation, the total required timescale for a sodium ion to complete a charge or discharge process may begiven as:t _(total)=(La/2)² /D _(electrolyte)+(d _(a)/2)² /D _(a)+(Ls)² /D_(s)+(Lc/2)² /D _(electrolyte)+(d _(c)/2)² /D _(c)   (1)where D_(electrolyte)=Na ion diffusion coefficient in electrolyte,D_(a)=Na ion diffusion coefficient in an anode active material particle,D_(s)=Na ion diffusion coefficient through a porous separator, andD_(c)=Na ion diffusion coefficient in a cathode active materialparticle.

Representative diffusion coefficients of Na⁺ in or through variousliquid mediums or solid membrane or particles are given below (based onopen literature data and our best estimates): liquid electrolyte (2×10⁻⁶cm²/s); separator (7.5×10⁻⁷ cm²/s); Na₄Mn₉O₁₈ (2×10⁻¹² cm²/s);NaV₁-xCrxPO₄F (10⁻¹³ to 10⁻¹⁰ cm²/s); and hard carbon anode (3×10⁻¹¹cm²/s).

This implies that, for a conventional sodium-ion battery cell whereinNa₄Mn₉O₁₈ particles are used as a cathode active material and solid hardcarbon (HC) particles (un-treated, non-porous, and not a type of thenanostructured disordered carbon in the present context), second term,(d_(a)/2)²/D_(a), and the final term, (d_(c)/2)²/D_(c), in Eq. (1)dictate the required total diffusion time due to the excessively lowsolid-state diffusion coefficients. As illustrated in FIG. 8(A), thetotal diffusion time for sodium ions to migrate from the anode activematerial to the cathode active material varies between 35.7 and 557minutes if the diameter of Na₄Mn₉O₁₈ particles increases from 0.01 μm(10 nm) to 5 μm.

By contrast, if the same Na₄Mn₉O₁₈ particles are used as a sodium sourceat the anode and functionalized graphene (f-NGP) is used as thenanostructured cathode material in a sodium super-battery or partiallysurface-enabled sodium ion-exchanging battery, the required diffusiontimes are reduced to less than 1 minute (if particle diameter is 0.01μm), as opposed to 35.7 minutes. If the diameters of the Na₄Mn₉O₁₈particles are maintained at 0.5 μm or smaller, the total diffusion timecan be below 7 minutes. This implies that the required battery re-chargetime is much shorter than 10 minutes, which conventional lithium-ion orsodium ion batteries thus far have not been able to achieve.

In this type of sodium ion super-battery, the cathode is a mesoporousstructure of a functionalized nanocarbon material (e.g., graphene, CNT,or disordered carbon), but Na₄Mn₉O₁₈ particles constitute the anode(schematically illustrated in FIG. 1(B)). In a battery dischargesituation, sodium ions must diffuse out of Na₄Mn₉O₁₈ particles, and thendiffuse in liquid electrolyte across the anode thickness. Subsequently,sodium ions must move (in liquid electrolyte) across a porous separator,diffuse across part of the cathode thickness in liquid electrolyte toreach a particular surface-borne functional group of a nanostructuredcathode active material. There is no need to undergo solid-statediffusion at the cathode side. The whole process is essentially dictatedby the solid-state diffusion at the anode.

The required diffusion times are even shorter if the anode contains a20-μm thick sodium foil (or some sodium powder) as a sodium ion sourcedisposed between a current collector and a porous separator layer 50 μmin thickness, and the cathode is composed of a nanostructured,functionalized CNT or NGP material. As illustrated in FIG. 8(B), such apartially surface-enabled, sodium ion-exchanging battery would require adiffusion time as short as 109 seconds (<2 minutes) when the cathodethickness is 200 μm. If the cathode thickness is reduced to 3 μm, thediffusion time is further reduced to 9.36 seconds.

In this type of sodium ion super-battery (partially surface-enabledbattery) containing a mesoporous cathode of a functionalized nanocarbonmaterial (e.g., graphene, CNT, or disordered carbon) and a sodium metalfoil as the anode (schematically illustrated in FIG. 1(C)), Na ions donot have to diffuse through a solid-state cathode particle and, hence,are not subject to the limitation by a low solid-state diffusioncoefficient at the cathode (e.g. 10⁻¹³-10⁻¹¹ cm²/s in asodium-transition metal oxide particle). Instead, the presently inventednanostructured cathode active materials are highly porous, allowingliquid electrolyte to reach the interior of the pores where thefunctional groups are present to readily and reversibly react withsodium ions that diffuse into these pores through a liquid medium (not asolid medium) with a high diffusion coefficient (e.g., 2×10⁻⁶ cm²/s). Insuch a sodium super-battery, the final term, (d_(c)/2)²/D_(c), in Eq.(1) is practically non-existing. The required total diffusion time isnow dictated by the thicknesses of the electrodes and the separator. Theabove discussion is based on the premise that the reversible reactionbetween a functional group and a sodium ion in the electrolyte is fast,and the whole charge-discharge process is not reaction-controlled.

Several significant observations can be made from the data of FIG. 8(A),FIG. 8(B), FIG. 9(A), FIG. 9(B) and related calculations:

-   -   (1) Conventional sodium ion batteries featuring a micron-sized        solid hard carbon particle anode (diameter=5 μm) and a        micron-sized Na₄Mn₉O₁₈ (particle diameter=5 μm) with an        electrode thickness of 100 μm would require 9.28 hours to        complete the required sodium ion diffusion process. This is why        conventional sodium ion batteries exhibit very low power        densities (typically 100-500 W/kg).    -   (2) In contrast, for one type of sodium super-batteries        featuring a functionalized carbon cathode (e.g. f-CNT, f-NGP, or        porous f-disordered carbon) and an anode of Na₄Mn₉O₁₈        nanoparticles (100 nm), the required diffusion times is 70 sec        (<1.2 minutes) for a cathode thickness of 100 μm. This is        30-fold faster than the conventional sodium-ion batteries with        the cathode particles having a diameter of 100 nm (diffusion        time=36 minutes).    -   (3) For the partially surface-enabled sodium super-batteries,        the electrode thickness and separator thickness are two        dominating factor. For instance, in the case of using sodium        metal foil as the anode (foil thickness=20 μm), the total        diffusion time can be as short as <10 sec (when the cathode        thickness is 0.3 μm or 3 μm and separator thickness is 50 μm),        which increases to 109 sec (still less than 2 minutes) when the        cathode thickness is 200 μm (FIG. 9(A)). If the separator        thickness can be reduced to 10 μm and the cathode thickness        reduced to 3 μm, the required diffusion time would be 1.33        seconds. The diffusion time would be further reduced to 0.6 sec        if the sodium foil thickness at the anode is reduced to 10 μm.        Such a short response time is unheard of even for conventional        supercapacitors that are noted for their fast response and,        hence, high power densities.    -   (4) As illustrated in FIG. 9(B), for a fully surface-enabled        battery with a 10-μm separator, 10-μm sodium source, 10-μm        nanostructured anode, and 10-μm nanostructured cathode, the        required diffusion time would be less than 0.4 seconds.    -   (5) The above observations imply that the sodium super-batteries        should have an extraordinary power density, particularly when        the electrodes are ultra-thin.        It may be noted that the above calculations for the        super-batteries (partially surface-enabled devices) containing a        sodium foil as the anode are applicable to the fully        surface-enabled battery device as well, with the exception that        the sodium foil thickness may be replaced with the thickness of        a nanostructured anode in the calculation. The sodium source        (sodium particles or pieces of sodium foil) would not add        additional anode thickness value in the calculations of the        required diffusion times since the nanostructured anode is        “elastic” or compressible. The sodium foil may be compressed        against the nanostructured anode, or the sodium particles may be        incorporated in the nanostructured anode when the battery device        is made. Once sodium particles or foil are ionized during the        first discharge cycle, the nanostructured anode (e.g. NGP or        CNT-based mat) would snap back to touch the separator. Based on        the above calculations, the required diffusion times for the        super-battery (partially surface-enabled) and those for the        fully surface-enabled battery should be approximately the same.        Then, why would the fully surface-enabled battery possibly be        better than the partially surface-enabled super-battery with a        sodium foil alone as the anode (without the nanostructured CNT        or NGP)?

The answer is related to the surface area of the electrode (particularlythe anode). The above-described calculations of the required diffusiontimes are based on the assumption that the electrodes have sufficientsurface areas to capture large amounts of sodium ions concurrently orwithin a very short period of time, particularly in a highcharge/discharge rate or high current density demand situation, furtherexplained below:

Fully Surface-Enabled Battery Device Versus Partially Surface-EnabledBattery

It may be noted that, for the first type of sodium super-battery orpartially surface-enabled sodium ion-exchanging battery (Na foil/f-CNT)where the anode is a sodium foil, there is no anode particle and, hence,no particle diameter (d_(a) was assigned as zero in the abovecalculation). During the first discharge, Na foil is electrochemicallyionized to release sodium ions. In the above calculations, thissurface-mediated reaction was assumed to be fast and not rate-limiting.In reality, this surface reaction can become rate-limiting when a highdischarge rate is required (i.e. when the external circuit or loaddemands a high current density). This limitation may not be controlledby the surface ionization rate itself, but instead by the limited amountof surface area of the lithium foil during the first discharge cycle. Inother words, at a given moment of time during the first discharge, thereis only so much surface area from which sodium ions can be releasedsimultaneously.

Additionally, during the re-charge cycle, sodium ions move back from thecathode to the anode side, trying to re-deposit onto a surface of theanode current collector (e.g. a copper foil), which is the only surfaceavailable at the anode of a super-battery. There are two serious issuesassociated with using a current collector alone to accommodate thein-flux of sodium ions during re-charge:

-   -   (1) If the re-charge rate is high (with a high current density),        the huge numbers of sodium ions that rapidly migrate back to the        anode side are all trying to deposit simultaneously onto the        surface of a current collector, which typically has a very low        surface area (specific surface area typically <<1 m²/g). This        limited surface area could become deposition rate-limiting.    -   (2) If the re-charge rate is low (with a low current density),        the returning sodium ions would find a way to deposit onto the        current collector surface in a non-uniform manner. Certain        favorable spots will receive more deposited sodium atoms first,        and these spots could continue to be deposited at a higher rate.        Such a non-uniform sodium deposition could lead to the formation        of dendrites at the anode, which could grow longer and longer as        the number of cycles increases, and eventually penetrate through        the separator to reach the cathode side, causing internal        shorting. This possibility could pose a similar problem that        plagued the lithium metal battery industry in late 1980s and        eventually resulted in the termination of essentially all the        lithium metal cell productions in early 1990s. We would not want        to see this potential internal shorting problem lead to the same        disastrous result for sodium ion-based batteries.        After an extensive and in-depth study, the applicants have        solved these two critical issues by implementing a        nanostructured anode between an anode current collector and a        porous separator. This nanostructured anode is preferably        composed of a nanocarbon material having a high specific surface        area, such as the nanographene platelet (NGP, single-layer        graphene or multi-layer graphene), carbon nanotube        (single-walled or multi-walled), carbon nanofiber (vapor-grown,        electrospun polymer derived, etc), porous disordered carbon,        metal nanowire, conductive nanowire, etc. The specific surface        area of this nanostructured anode is preferably greater than 100        m²/g, more preferably greater than 500 m²/g, further preferably        greater than 1,000 m²/g, and most preferably greater than 1,500        m²/g. This nanostructured material preferably has a functional        surface having thereon a functional group that reversibly reacts        with an alkali atom or ion (e.g., sodium atom or ion),        alkaline-earth metal, transition metal, and other metal ions        (e.g. Al).

It is very surprising for us to observe that the implementation of thisnanostructured anode significantly increases not only the power density(Kw/kg), but also the energy density (Wh/kg) of the presently inventedsurface-enabled, metal ion-exchanging battery device. We were reallyvery surprised to observe these highly significant observations(presented in the Examples of this specification). Not wishing to belimited by the theory, but we believe that this newly implementednanostructured anode plays at least the following three roles:

-   -   (1) During the re-charge cycle, the massive surface areas of        this nanostructured anode enable huge numbers of metal ions to        be rapidly deposited simultaneously in a high current density        situation (high charge rate). This makes it possible for the        battery device to be re-charged in seconds or fractions of a        second. This has not been possible with any prior art lithium        metal or lithium ion battery, any prior art lithium        super-battery, or any prior art sodium-ion battery.    -   (2) During the first discharge operation of a freshly made        surface-enabled battery device of the instant invention, the        sodium foil or sodium particles, as examples of an alkali ion        source, get ionized, releasing alkali ions at the anode which        travel into the cathode side and get captured by the functional        material surfaces of the cathode. Upon re-charging, these alkali        ions return to the anode and uniformly deposit onto the massive        surfaces of the nanostructured anode, forming an ultra-thin        coating of alkali metal (possibly mono-layer) thereon. Such a        huge surface area of alkali-decorated functional surfaces        enables simultaneous release of great amounts of alkali ions        during subsequent discharge cycles. This concurrent, massive        releasing of alkali ions had not been possible in a battery with        an anode current collector alone whose specific surface area is        normally much less than 1 m²/g. The high specific surface area        of the nanostructured anode, >>100 m²/g, enables both fast        charging and fast discharging, achieving an unprecedented power        density.    -   (3) The nanostructured anode, electronically connected to a        current collector, also provides a uniform electric field in the        anode space, allowing the returning metal ions to more        homogeneously deposit onto the surface of nanomaterials (e.g.        graphene or CNT). Since huge surface areas are available for        this purpose, only an extremely small amount of metal atoms is        deposited onto any single spot, insufficient for the growth of a        dendrite. These reasons imply that the presently invented        surface-enabled battery device is a safer energy storage device.        Surface-Enabled, Sodium Ion-Exchanging Battery Device Versus        Prior Art Supercapacitors

This new fully surface-enabled, metal ion-exchanging battery device isalso patently distinct from the conventional supercapacitor thatoperates on the electric double layer (EDL) mechanism orpseudo-capacitance mechanism. In both conventional mechanisms, no metalions are exchanged between the two electrodes. In particular, our newbattery device is patently distinct from the LBL CNT-based symmetricsupercapacitor of Lee, et al [Nature Nanotechnology, 5 (2010) 531-537],wherein both the anode and the cathode are ultra-thin CNT structuresprepared by the layer-by-layer (LBL) process. This symmetricsupercapacitor does not contain an extra lithium source or alkali sourceand does not involve exchange of lithium or alkali ions between the twoelectrodes.

Examples of Nanostructured Electrode Materials

Nanostructured materials for use in the anode or cathode of the instantinvention may preferably contain nanographene platelet (NGP), carbonnanotube (CNT), or nanostructured or porous disordered carbon. Thesenanostructured carbon materials can be used as a supporting substratefor other organic or polymeric functional materials that have usefulfunctional groups (e.g., carbonyl) but are not electrically conducting.The CNT is a better known material in the nanomaterial industry and,hence, will not be further discussed herein. What follows is adescription of NGP and nanostructured disordered carbon:

Nano Graphene Platelet (NGP)

An NGP is a single-layer graphene sheet or a stack of several graphenesheets with each sheet being a hexagonal structure of carbon atoms(single layer being as thin as 0.34 nm or one atom thick). Theapplicant's research group was the first in the world to discoversingle-layer graphene [B. Z. Jang and W. C. Huang, “Nano-scaled GraphenePlates,” U.S. patent application Ser. No. 10/274,473 (Oct. 21, 2002);now U.S. Pat. No. 7,071,258 (Jul. 4, 2006)] and the first to usegraphene for supercapacitor [L. Song, A. Zhamu, J. Guo, and B. Z. Jang“Nano-scaled Graphene Plate Nanocomposites for SupercapacitorElectrodes” U.S. patent application Ser. No. 11/499,861 (Aug. 7, 2006),now U.S. Pat. No. 7,623,340 (Nov. 24, 2009)], and for lithium-ionbattery applications [A. Zhamu and B. Z. Jang, “Nano GraphenePlatelet-Based Composite Anode Compositions for Lithium Ion Batteries,”U.S. patent application Ser. No. 11/982,672 (Nov. 5, 2007), now U.S.Pat. No. 7,745,047 (Jun. 29, 2010)].

For the purpose of defining the geometry of an NGP (includingnon-oxidized graphene and graphene oxide), the NGP is described ashaving a length (the largest dimension), a width (the second largestdimension), and a thickness. The thickness is the smallest dimension,which is no greater than 100 nm and, in the present application, nogreater than 10 nm (preferably no greater than 5 nm and most preferablysingle-layer graphene, including graphene oxide, with a thickness ofapproximately 0.34-1.2 nm). When the platelet is approximately circularin shape, the length and width are referred to as diameter. In thepresently defined NGPs, there is no limitation on the length and width,but they are preferably smaller than 10 μm and more preferably smallerthan 1 μm. We have been able to produce NGPs with length smaller than100 nm or larger than 10 μm. The NGP can be pristine graphene (withessentially 0% oxygen content) or graphene oxide (with up toapproximately 45% by weight oxygen). Graphene oxide can be thermally orchemically reduced to become reduced graphene oxide (typically with anoxygen content of 1-20%). For use in the anode and/or the cathode of thelithium super-battery, the oxygen content is preferably in the range of5% to 30% by weight, and more preferably in the range of 10% to 30% byweight.

Despite the fact that individual graphene sheets have an exceptionallyhigh specific surface area, flat-shaped graphene sheets prepared byconventional routes have a great tendency to re-stack together oroverlap with one another, thereby dramatically reducing the specificsurface area that is accessible by the electrolyte. FIG. 7 shows a newbreed of graphene that is herein referred to as the curved grapheneplatelet or sheet. Curved NGPs are capable of forming a mesoporousstructure having a desired pore size range (e.g. slightly >2 nm) whenthey were stacked together to form an electrode. This size range allowsthe commonly used metal ion-containing electrolytes to enter the poresbetween graphene sheets and edges so that the metal ions (sodium ions,calcium ions, zinc ions, aluminum ions, etc) can simply swim throughliquid electrolyte to reach and rapidly react/interact withsurface-borne functional groups. These surface-borne functional groupsare on a graphene plane surface or an edge surface, which is in directcontact with liquid electrolyte. The metal ions are not required toundergo solid-state diffusion (intercalation) in order to be stored in ananostructured or porous NGP electrode (or released from this electrode)and, hence, such an electrode is said to be surface-mediated or surfaceenabled.

The curved NGPs may be produced by using the following recommendedprocedures:

-   (a) dispersing or immersing a laminar graphite material (e.g.,    natural graphite powder) in a mixture of an intercalant and an    oxidant (e.g., concentrated sulfuric acid and nitric acid,    respectively) to obtain a graphite intercalation compound (GIC) or    graphite oxide (GO);-   (b) exposing the resulting GIC or GO to a thermal shock, preferably    in a temperature range of 600-1,100° C. for a short period of time    (typically 15 to 60 seconds), to obtain exfoliated graphite or    graphite worms (some oxidized NGPs with a thickness <100 nm could be    formed at this stage if the intercalation/oxidation step was allowed    to proceed for a sufficiently long duration of time; e.g. >24    hours);-   (c) dispersing the exfoliated graphite to a liquid medium containing    a functionalizing agent (e.g., an oxidizing agent such as sulfuric    acid, nitric acid, hydrogen peroxide or, preferably, carboxylic    acid, formic acid, etc., which is a source of —COOH group) to form a    suspension. Stirring, mechanical shearing, or ultrasonication,    and/or temperature can be used to break up graphite worms to form    separated/isolated NGPs and/or to help attach desired functional    groups to the oxidized NGPs, resulting in the formation of    functionalized NGPs. The functionalizing agent may be an amine- or    —NH₂-containing group, as used in several common curing agents for    epoxy resins; and, optionally,-   (d) aerosolizing the graphene-liquid solution into liquid droplets    containing chemically functionalized single or multiple NGPs while    concurrently removing the liquid to recover curved NGPs containing    desired functional groups. Without the aerosolizing step, the    resulting functionalized graphene platelets tend to be flat-shaped.

It may be noted that steps (a) to (b) are the most commonly used stepsto obtain exfoliated graphite and graphene oxide platelets in the field.Step (c) is designed for imparting additional functional groups to NGPs.Step (d) is essential to the production of curved graphene sheets.Oxidized NGPs or GO platelets may be chemically reduced to recoverconductivity properties using hydrazine as a reducing agent, before,during, or after chemical functionalization.

The carboxylic acids, being environmentally benign, are particularlypreferred functionalizing agents for imparting carbonyl or carboxylicgroups to NGPs. The carboxylic acid may be selected from the groupconsisting of aromatic carboxylic acid, aliphatic or cycloaliphaticcarboxylic acid, straight chain or branched chain carboxylic acid,saturated and unsaturated monocarboxylic acids, dicarboxylic acids andpolycarboxylic acids that have 1-10 carbon atoms, alkyl esters thereof,and combinations thereof. Preferably, the carboxylic acid is selectedfrom the group consisting of saturated aliphatic carboxylic acids of theformula H(CH₂)_(n)COOH, wherein n is a number of from 0 to 5, includingformic, acetic, propionic, butyric, pentanoic, and hexanoic acids,anhydrides thereof, reactive carboxylic acid derivatives thereof, andcombinations thereof. The most preferred carboxylic acids are formicacid and acetic acid.

The NGPs used in the aforementioned electrode may be subjected to thefollowing treatments, separately or in combination, before or after thefunctionalization operation:

-   -   (i) chemically functionalized with a different functional group.        Other useful surface functional groups may include quinone,        hydroquinone, quaternized aromatic amines, or mercaptans;    -   (ii) coated or grafted with a polymer that contains a desired        functional group (e.g., carbonyl group);    -   (iii) subjected to an activation treatment (analogous to        activation of carbon black materials) to create additional        surfaces and possibly imparting functional chemical groups to        these surfaces. The activation treatment can be accomplished        through CO₂ physical activation, KOH chemical activation, or        exposure to nitric acid, fluorine, or ammonia plasma.

The above-described processes produce graphene oxide platelets oroxidized NGPs. The heavy oxidation step involved in these processesintrinsically introduces oxygen-containing groups to both the edgesurfaces and the basal plane surfaces (top and bottom surfaces) of anNGP. This can be good or bad. On the one hand, we would like to createas many functional groups as possible to maximize the lithium-capturingcapacity. But, on the other hand, the functional groups on the basal orgraphene plane necessarily inflict damage to the plane and significantlyreduce the over-all conductivity of an NGP. The formation of functionalgroups in this manner, without step (c) above, is not a well-controlledprocess.

Fortunately, after very diligent research work, we have discovered analternative way to impart functional groups to NGPs in a more controlledmanner. This new way involves producing pristine NGPs without goingthrough the conventional chemical intercalation/oxidation procedure. Theproduced non-oxidized graphene (naturally having edge surfaces beingmore chemically active) is then subjected to controlled oxidation orcontrolled functionalization. We have surprisingly found that functionalgroups were attached to the edge surfaces first and essentiallyexhausted the active sites at the edge surfaces before any significantamount of functional groups began to attach themselves to the basalplanes.

In 2007, we reported a direct ultrasonication method of producingpristine nanographene directly from graphite particles dispersed in asurfactant-water suspension [A. Zhamu, et al, “Method of ProducingExfoliated Graphite, Flexible Graphite, and Nano-Scaled GraphenePlates,” U.S. patent application Ser. No. 11/800,728 (May 8, 2007) nowU.S. Pat. No. 7,824,651 (Nov. 2, 2010)]. This method entails dispersingnatural graphite particles in a low surface tension liquid, such asacetone or hexane. The resulting suspension is then subjected to directultrasonication for 10-120 minutes, which produces graphene at a rateequivalent to 20,000 attempts to peel off graphene sheets per second perparticle. The graphite has never been intercalated or oxidized and,hence, requires no subsequent chemical reduction. This method is fast,environmentally benign, and can be readily scaled up, paving the way tothe mass production of pristine nanographene materials. The same methodwas later studied by others and now more commonly referred to as the“liquid phase production.” Once pristine graphene is produced, thematerial is then exposed to an oxidation or functionalization treatmentusing, for example, a gaseous-phase or liquid acid or acid mixture. Thepristine NGPs may also be immersed in carboxylic acids at a desiredtemperature for a period of time to obtain NGPs with a desired level offunctionalization.

Specifically, the oxidation treatment comprises subjecting the pristineNGP material to an oxidizing agent preferably selected from ozone,sulfonic (SO₃) vapor, an oxygen-containing gas, hydrogen peroxide vapor,nitric acid vapor, or a combination thereof. Preferably, the treatmentcomprises subjecting the pristine NGP material to an oxidizing agent ina hydrogen-containing environment. Although oxidation treatment can beconducted by immersing NGPs in a liquid acid and/or oxidizerenvironment, such a procedure requires a subsequent water-rinsing andpurification step (such a rinsing procedure is not as tedious asrequired in the case of conventional sulfuric acid-intercalationgraphite, nevertheless). Hence, a gaseous treatment requiring nopost-treatment rinsing is preferred.

A primary goal of the oxidation treatment is to impart a desired amountof functional groups to pristine NGPs without a significant compromisein electrical conductivity. After an extensive and in-depth study wehave come to discover that conductive functionalized NGPs can beproduced with an oxygen content no greater than 25% by weight,preferably between 5% and 25% by weight. Presumably, a majority of thefunctional groups are located at the edge surfaces of NGPs since theelectrical conductivity would not be significantly reduced. Beyond 25%of over-all oxygen content, functional groups begin to appear ongraphene plane surfaces, interrupting electron-conducting paths. Theoxygen contents were determined using chemical elemental analysis andX-ray photoelectron spectroscopy (XPS).

The partially oxidized NGPs prepared according to a preferred embodimentof the present invention can be further functionalized by carrying outan additional step of contacting the partially oxidized NGPs with areactant so that a functional group is added to a surface or edge of thenanographene platelet. The functional group may contain alkyl or arylsilane, alkyl or aralkyl group, hydroxyl group, amine group,fluorocarbon, or a combination thereof.

The NGPs, after a partial oxidation treatment, will have a reactivegraphene surface (RGS) or reactive graphene edge (RGE). They can beprescribed to undergo the following reactions:RGS/RGE+CH₂══CHCOX (at 1,000° C.)→Graphene-R′COH (where X=—OH, —Cl, or—NH₂); e.g., RGS/RGE+CH₂══CHCOOH→G-R′CO—OH (where G=graphene);  (a)RGS/RGE+Maleic anhydride→G-R′(COOH)₂;  (b)RGS/RGE+CH₂══CH—CH₂X→G-R′CH₂X (where X=—OH, -halogen, or —NH₂);  (c)RGS/RGE+H₂O→G==O (Quinoidal);  (d)RGS/RGE+CH₂══CHCHO→G-R′CHO (Aldehydic);  (e)

In the above-listed reactions, R′ is a hydrocarbon radical (alkyl,cycloalkyl, etc). Partial oxidation of pristine NGPs can lead to theattachment of some functional groups on a surface or at an edge of agraphene plane, including carboxylic acid and hydroxyl groups. A largenumber of derivatives can be prepared from carboxylic acid alone. Forinstance, alcohols or amines can be easily linked to acid to providestable esters or amides.

Any reaction capable of attaching carbonyl (>C═O) or amine (—NH₂) groupto the graphene edge or basal plane surface may be used for practicingthe instant invention.

We have also surprisingly observed that the surface of a graphene sheet,basically made up of a layer of carbon atoms arranged in a hexagonal orhoneycomb-like structure, can also allow metal ions to adsorb thereon ina fast and reversible manner. Such a mono-layer of metal atoms (e.g.sodium, calcium, titanium, or aluminum atoms) appears to be sufficientlystable so that metal atom-adsorbed graphene surfaces, if used as ananode active material, would not lead to any significant self-discharge.When used at the cathode, the metal atoms adsorbed thereon can bereadily released during the battery re-charging cycle, enabling a fastre-charging.

This ease of releasing metal ions is in sharp contrast to theconventional metal-air or Li—S cells wherein, during re-charge of abattery, the reduction of metal oxide (e.g. lithium oxide) or metalsulfide (e.g., Li_(x)S) is an extremely difficult and slow process evenwith the assistance of currently the best and most expensiveelectro-catalysts (e.g., Pt, Pd, etc.). Furthermore, currently, theround trip efficiency of Li-air cells is typically in the range of30-70% (mostly <50%). By contrast, the round trip efficiency of thepresently invented graphene-mediated cell is typically close to 100%.State-of-the-art Li-air cells can only be used for a small number ofcycles (typically <50 cycles), but our surface-enabled devices arecapable of cycling for tens or hundreds of thousands of cycles.

Nanostructured or Porous Disordered Carbon

The disordered carbon material may be selected from a broad array ofnanostructured or mesoporous carbonaceous materials, such as mesoporoussoft carbon, hard carbon, polymeric carbon (or carbonized resin),mesophase carbon, coke, carbonized pitch, carbon black, activatedcarbon, or partially graphitized carbon. As schematically illustrated inFIG. 5(A) and FIG. 5(B), a disordered carbon material is typicallyformed of two phases wherein a first phase is small graphite crystal(s)or small stack(s) of graphite planes (with typically up to 10 graphiteplanes or aromatic ring structures overlapped together to form a smallordered domain) and a second phase is non-crystalline carbon, andwherein the first phase is dispersed in the second phase or bonded bythe second phase. These graphite crystals and stacks of graphite planesare nano-sized, both in the thickness dimension and often in the lateraldimensions as well. The second phase is made up of mostly smallermolecules, smaller aromatic rings, defects, and amorphous carbon. Thedesired functional groups (e.g., —COOH, >C═O, and NH₂ groups in FIG.5(B)) are attached to an edge or plane surface of an aromatic ringstructure. However, without a special activation or chemical treatmentas herein described, solid particles of disordered carbon either do nothave pores or have pores that are too small to allow liquid electrolyteto enter the interior of a particle and, hence, the functional groupscannot be accessed by the metal ions residing in electrolyte.

Hence, the disordered carbon must be treated to become highly porous(e.g., activated carbon) or present in an ultra-fine powder form(preferably having a dimension less than 5 nm or having a specificsurface area higher than 10 m²/g, preferably higher than 100 m²/g, morepreferably higher than 500 m²/g, further preferably higher than 1,000m²/g, and most preferably higher than 1,500 m²/g). Solid particles ofconventional carbon black, soft carbon, and hard carbon, etc, typicallyrequire a special activation or chemical treatment to open up the pores(preferably >2 nm in size) that enable liquid electrolyte to permeateinto the interior of these disordered materials, as illustrated in FIG.6(D). In other words, without these pores (particularly mesoscaledpores, >2 nm), liquid electrolyte would not be able to reach theinterior of a particle of carbon black, soft carbon, or hard carbon andthe metal ions would not be able to access the surface-borne functionalgroups that mostly exist inside the particles. In such pore-freesituations, metal ions would have to intercalate or diffuse into thebulk of a carbon black particle (this electrode would not besurface-enabled). The nanostructured disordered carbon refers to adisordered carbon material with pores that serve as gates through whichliquid electrolyte can access the interior of the material.

With the gates being open, the porous or nanostructured disorderedcarbon would have functional groups (FIG. 5(C)) capable of undergoing asurface redox reaction or forming a chemical complex with incomingalkali ions floating in the liquid electrolyte that permeates into theinterior of an electrode material particle.

Soft carbon refers to a carbonaceous material composed of small graphitecrystals wherein the orientations of these graphite crystals or stacksof graphene sheets are conducive to further merging of neighboringgraphene sheets or further growth of these graphite crystals or graphenestacks (FIG. 6(A)) using a high-temperature heat treatment(graphitization). Hence, soft carbon is said to be graphitizable.

Hard carbon (FIG. 6(B)) refers to a carbonaceous material composed ofsmall graphite crystals wherein these graphite crystals or stacks ofgraphene sheets are not oriented in a favorable directions (e.g. nearlyperpendicular to each other) and, hence, are not conducive to furthermerging of neighboring graphene sheets or further growth of thesegraphite crystals or graphene stacks (i.e., not graphitizable).

As schematically illustrated in FIG. 6(C), Carbon black (CB), acetyleneblack (AB), and activated carbon (AC) are typically composed of domainsof aromatic rings or small graphene sheets, wherein aromatic rings orgraphene sheets in adjoining domains are somehow connected through somechemical bonds in the disordered phase (matrix). These carbon materialsare commonly obtained from thermal decomposition (heat treatment,pyrolyzation, or burning) of hydrocarbon gases or liquids, or naturalproducts (wood, coconut shells, etc).

The preparation of polymeric carbons by simple pyrolysis of polymers orpetroleum/coal tar pitch materials has been known for approximatelythree decades. When polymers such as polyacrylonitrile (PAN), rayon,cellulose and phenol formaldehyde were heated above 300° C. in an inertatmosphere they gradually lost most of their non-carbon contents. Theresulting structure is generally referred to as a polymeric carbon.Depending upon the heat treatment temperature (HTT) and time, polymericcarbons can be made to be insulating, semi-conducting, or conductingwith the electric conductivity range covering approximately 12 orders ofmagnitude. This wide scope of conductivity values can be furtherextended by doping the polymeric carbon with electron donors oracceptors. These characteristics uniquely qualify polymeric carbons as anovel, easy-to-process class of electro-active materials whosestructures and physical properties can be readily tailor-made.

Polymeric carbons can assume an essentially amorphous structure, or havemultiple graphite crystals or stacks of graphene planes dispersed in anamorphous carbon matrix. Depending upon the HTT used, variousproportions and sizes of graphite crystals and defects are dispersed inan amorphous matrix. Various amounts of two-dimensional condensedaromatic rings or hexagons (precursors to graphene planes) can be foundinside the microstructure of a heat treated polymer such as a PAN fiber.An appreciable amount of small-sized graphene sheets are believed toexist in PAN-based polymeric carbons treated at 300-1,000° C. Thesespecies condense into wider aromatic ring structures (larger-sizedgraphene sheets) and thicker plates (more graphene sheets stackedtogether) with a higher HTT or longer heat treatment time (e.g., >1,500°C.). These graphene platelets or stacks of graphene sheets (basalplanes) are dispersed in a non-crystalline carbon matrix. Such atwo-phase structure is a characteristic of some disordered carbonmaterial.

There are several classes of precursor materials to the disorderedcarbon materials of the instant patent application. For instance, thefirst class includes semi-crystalline PAN in a fiber form. As comparedto phenolic resin, the pyrolized PAN fiber has a higher tendency todevelop small crystallites that are dispersed in a disordered matrix.The second class, represented by phenol formaldehyde, is a moreisotropic, essentially amorphous and highly cross-linked polymer. Thethird class includes petroleum and coal tar pitch materials in bulk orfiber forms. The precursor material composition, heat treatmenttemperature (HTT), and heat treatment time (Htt) are three parametersthat govern the length, width, thickness (number of graphene planes in agraphite crystal), and chemical composition of the resulting disorderedcarbon materials.

In the present investigation, PAN fibers were subjected to oxidation at200-350° C. while under a tension, and then partial or completecarbonization at 350-1,500° C. to obtain polymeric carbons with variousnano-crystalline graphite structures (graphite crystallites). Selectedsamples of these polymeric carbons were further heat-treated at atemperature in the range of 1,500-2,000° C. to partially graphitize thematerials, but still retaining a desired amount of amorphous carbon (noless than 10%). Phenol formaldehyde resin and petroleum and coal tarpitch materials were subjected to similar heat treatments in atemperature range of 500 to 1,500° C. The disordered carbon materialsobtained from PAN fibers or phenolic resins are preferably subjected toactivation using a process commonly used to produce activated carbon(e.g., treated in a KOH melt at 900° C. for 1-5 hours). This activationtreatment is intended for making the disordered carbon mesoporous,enabling chemical functionalizing agents to reach the edges or surfacesof the constituent aromatic rings. The mesopores will also be accessibleto the liquid electrolyte after the battery cell is made. Such anarrangement enables the lithium ions in the liquid to readily react withthe functional groups without having to undergo solid-state diffusion.

Certain grades of petroleum pitch or coal tar pitch may be heat-treated(typically at 250-500° C.) to obtain a liquid crystal-type, opticallyanisotropic structure commonly referred to as mesophase. This mesophasematerial can be extracted out of the liquid component of the mixture toproduce mesophase particles or spheres.

The functionalized disordered carbon may be produced by using thefollowing recommended procedures (as a preferred embodiment):

-   (e) Physically or chemically activating a desired disordered carbon    (e.g. a soft carbon, hard carbon, polymeric carbon or carbonized    resin, mesophase carbon, coke, carbonized pitch, carbon black,    activated carbon, or partially graphitized carbon) to obtain    activated disordered carbon that is now porous or nanostructured.    For instance, the activation treatment can be accomplished through    oxidizing, CO₂ physical activation, KOH or NaOH chemical activation,    or exposure to nitric acid, fluorine, or ammonia plasma. The main    purpose of this treatment is to create pores or open up gates    through which liquid electrolyte can enter to reach the interior of    a disordered carbon particle, allowing metal ions residing in the    liquid electrolyte to reach functional groups inside the    nanostructured material. This obviates the need for metal ions to    undergo solid-state diffusion (intercalation) and, hence, the metal    ion storage in a nanostructured or porous disordered carbon    electrode is said to be surface-mediated or surface-enabled.-   (f) dispersing the activated disordered carbon to a liquid medium    containing a functionalizing agent (e.g., an oxidizing agent such as    sulfuric acid, nitric acid, hydrogen peroxide or, preferably,    carboxylic acid, formic acid, etc., which is a source of —COOH    group) to form a suspension. Stirring, mechanical shearing, or    ultrasonication, and/or temperature can be used to break up the    activated disordered carbon particles to accelerate the    functionalization of disordered carbon. The functionalizing agent    may be an amine- (or —NH₂-containing group, as used in several    common curing agents for epoxy resins), carboxylic groups (—COOH),    or other groups capable of reversibly reacting with lithium; and,    optionally,-   (g) aerosolizing the suspension into liquid droplets containing    chemically functionalized disordered carbon particles while    concurrently removing the liquid to recover functionalized    disordered carbon particles.

The functionalizing procedures for nanostructured disordered carbon aresimilar to those used for NGPs and, hence, will not be repeated here. Inparticular, any reaction capable of attaching carbonyl (>C═O) or amine(—NH₂) group to the graphene edge or basal plane surface of a disorderedcarbon material may be used for practicing the instant invention.

Organic and Polymeric Functional Materials Containing Metal Ion-ReactingFunctional Groups

We have surprising found that many organic- or polymer-based functionalmaterials may contain pendant functional groups that are capable ofrapidly and reversibly reacting with alkali ions (in addition to lithiumions) in liquid or gel electrolyte. Examples includePoly(2,5-dihydroxy-1,4-benzoquinone-3,6-methylene) (PDBM), Li_(x)C₆O₆(x=1-3), Li₂(C₆H₂O₄), Li₂C₈H₄O₄ (Li terephthalate), Li₂C₆H₄O₄(Litrans-trans-muconate), 3,4,9,10-perylenetetracarboxylicacid-dianhydride(PTCDA) sulfide polymer, PTCDA,1,4,5,8-naphthalene-tetracarboxylicacid-dianhydride (NTCDA),Benzene-1,2,4,5-tetracarboxylic dianhydride, 1,4,5,8-tetrahydroxyanthraquinon, Tetrahydroxy-p-benzoquinone, and combinations thereof.These functional molecules, polymers, or salts normally have arelatively low electronic conductivity making them not amenable toserving as an electrode material by themselves. One exception issulfur-cross-linked PTCDA (PTCDA sulfide polymer).

Any of these non-conducting functional materials may be preferablycombined with (e.g. chemically bonded or attached to) a nanostructuredmaterial, such as the NGP, CNT, disordered carbon, nanowire, andnanofiber. For instance, both graphene and the constituent aromaticrings of a nanostructured disordered carbon (soft carbon, hard carbon,activated carbon, carbon black, etc) can have, on their edges orsurfaces, functional groups that can react with the matting functionalgroups on the aforementioned functional materials (e.g. the hydroxylgroup on Tetrahydroxy-p-benzoquinone). Alternatively, these organic orpolymeric functional materials may be simply supported on a surface of ananostructured material (e.g., graphene or nanowire surface). Thenanostructure material (e.g. graphene and disordered carbon) may befunctionalized as well so that it provides not only support for theorganic or polymeric material (imparting electric conductivity) but alsofunctional groups capable of reacting with alkali ions.

Electrolytes

A wide range of electrolytes can be used for practicing the instantinvention. Most preferred are non-aqueous liquid and polymer gelelectrolytes although other types can be used. The non-aqueouselectrolyte to be employed herein may be produced by dissolving anelectrolytic salt of a desirable metal ion or more than one type of ions(e.g. salt of combined Na⁺ and K⁺) in a non-aqueous solvent. Any knownnon-aqueous solvent which has been employed as a solvent for a lithiumsecondary battery can be employed. A non-aqueous solvent mainlyconsisting of a mixed solvent comprising ethylene carbonate (EC) and atleast one kind of non-aqueous solvent whose melting point is lower thanthat of aforementioned ethylene carbonate (hereinafter referred to as asecond solvent) may be preferably employed. This non-aqueous solvent isadvantageous in that it is (a) stable against a negative electrodecontaining a nanostructured carbonaceous material; (b) effective insuppressing the reductive or oxidative decomposition of electrolyte; and(c) high in conductivity. A non-aqueous electrolyte solely composed ofethylene carbonate (EC) is advantageous in that it is relatively stableagainst decomposition through a reduction by a carbonaceous material.However, the melting point of EC is relatively high, 39 to 40° C., andthe viscosity thereof is relatively high, so that the conductivitythereof is low, thus making EC alone unsuited for use as a secondarybattery electrolyte to be operated at room temperature or lower. Thesecond solvent to be used in a mixture with EC functions to make theviscosity of the solvent mixture lower than that of EC alone, therebypromoting the ion conductivity of the mixed solvent.

Preferred second solvents are dimethyl carbonate (DMC), methylethylcarbonate (MEC), diethyl carbonate (DEC), methyl butyrate (MB), ethylpropionate, methyl propionate, propylene carbonate (PC), γ-butyrolactone(γ-BL), acetonitrile (AN), ethyl acetate (EA), propyl formate (PF),methyl formate (MF), toluene, xylene and methyl acetate (MA). Thesesecond solvents may be employed singly or in a combination of two ormore. More desirably, this second solvent may be selected so that theviscosity of this second solvent is 28 cps or less at 25° C. Actually,these solvents can be used as a primary solvent with or without EC.

The mixing ratio of the aforementioned ethylene carbonate in the mixedsolvent should preferably be 10 to 80% by volume. If the mixing ratio ofthe ethylene carbonate falls outside this range, the conductivity of thesolvent may be lowered or the solvent tends to be more easilydecomposed, thereby deteriorating the charge/discharge efficiency. Morepreferable mixing ratio of the ethylene carbonate is 20 to 75% byvolume. When the mixing ratio of ethylene carbonate in a non-aqueoussolvent is increased to 20% by volume or more, the solvating effect ofethylene carbonate to lithium ions will be facilitated and the solventdecomposition-inhibiting effect thereof can be improved.

Examples of preferred mixed solvent are a composition comprising EC andMEC; comprising EC and MB; comprising EC, PC and MEC; comprising EC, MECand DEC; comprising EC, MEC and DMC; and comprising EC, MEC, PC and DEC;with the volume ratio of MEC being controlled within the range of 30 to80%. By selecting the volume ratio of MEC from the range of 30 to 80%,more preferably 40 to 70%, the conductivity of the solvent can beimproved.

The electrolytic salts to be incorporated into a non-aqueous electrolytemay be selected from a lithium salt, sodium salt, potassium salt,calcium salt, magnesium salt, zinc salt, titanium salt, any transitionmetal salt, aluminum salt, etc. Examples are lithium perchlorate(LiClO₄), sodium perchlorate (NaClO₄), potassium perchlorate (KClO₄),lithium hexafluorophosphate (LiPF₆), sodium hexafluorophosphate (NaPF₆),potassium hexafluorophosphate (KPF₆), transition metalhexafluorophosphate, aluminum hexafluorophosphate (Al(PF₆)₃), lithiumborofluoride (LiBF₄), sodium borofluoride (NaBF₄), potassiumborofluoride (KBF₄), calcium borofluoride (Ca(BF₄)₂), aluminumborofluoride (Al(BF₄)₃), transition metal borofluoride, alkaline-earthmetal borofluoride, lithium hexafluoroarsenide (LiAsF₆), other alkalimetal hexafluoroarsenides, transition metal hexafluoroarsenides, othermetal hexafluoroarsenides, lithium trifluoro-metasulfonate (LiCF₃SO₃)and bis-trifluoromethyl sulfonylimide lithium [LiN(CF₃SO₂)₂]. Amongthem, NaPF₆, NaBF₄, KPF₆, KBF₄ and NaN(CF₃SO₂)₂ are preferably used in asodium ion- or potassium ion-exchanging battery device. NaPF₆, NaBF₄,KPF₆, and KBF₄ are preferably used in a sodium ion- or potassiumion-exchanging battery device. NaPF₆, NaBF₄, KPF₆, and KBF₄, and/or analkaline-earth metal borofluoride are preferably used in analkaline-earth metal ion-exchanging battery device. Al(BF₄)₃, NaPF₆,NaBF₄, KPF₆, and KBF₄, are preferably used in an aluminum ion-exchangingbattery device, etc. The content of aforementioned electrolytic salts inthe non-aqueous solvent is preferably 0.5 to 2.0 mol/l.

The following examples serve to illustrate the preferred embodiments ofthe present invention and should not be construed as limiting the scopeof the invention:

Example 1: NGPs from Sulfuric Acid Intercalation and Exfoliation ofMCMBs

MCMB 2528 microbeads (Osaka Gas Chemical Company, Japan) have a densityof about 2.24 g/cm³; a median size of about 22.5 microns, and aninter-planar distance of about 0.336 nm. MCMB 2528 (10 grams) wereintercalated with an acid solution (sulfuric acid, nitric acid, andpotassium permanganate at a ratio of 4:1:0.05) for 24 hours. Uponcompletion of the reaction, the mixture was poured into deionized waterand filtered. The intercalated MCMBs were repeatedly washed in a 5%solution of HCl to remove most of the sulfate ions. The sample was thenwashed repeatedly with deionized water until the pH of the filtrate wasneutral. The slurry was dried and stored in a vacuum oven at 60° C. for24 hours. The dried powder sample was placed in a quartz tube andinserted into a horizontal tube furnace pre-set at a desiredtemperature, 600° C. for 30 seconds to obtain exfoliated graphite. Theexfoliated MCMB sample was subjected to further functionalization informic acid a 25° C. for 30 minutes in an ultrasonication bath to obtainfunctionalized graphene (f-NGP).

Graphene oxide solution was prepared by immersing natural graphitepowder (average particle size <100 μm) in an acid solution (sulfuricacid, nitric acid, and potassium permanganate at a ratio of 4:1:0.05)for 96 hours. The resulting yellow-brown color solution was rinsed andtreated using a centrifuge device to remove non-oxidized particles andexcess acids and oxidizers. The product was a gel-like solution withgraphene oxide polymers dissolved or dispersed in water.

Example 2: Preparation of Nanostructured, Functionalized Soft Carbon(One Type of Disordered Carbon)

Functionalized soft carbon was prepared from a liquid crystallinearomatic resin. The resin was ground with a mortar, and calcined at 900°C. for 2 h in a N₂ atmosphere to prepare the graphitizable carbon orsoft carbon. The resulting soft carbon was mixed with small tablets ofKOH (four-fold weight) in an alumina melting pot. Subsequently, the softcarbon containing KOH was heated at 750° C. for 2 h in N₂. Upon cooling,the alkali-rich residual carbon was washed with hot water until theoutlet water reached a pH value of 5-7. The activated soft carbon(porous and nanostructured) was then immersed in a 90% H₂O₂-10% H₂Osolution at 45° C. for an oxidation treatment that lasted for 2 hours.Then, the resulting partially oxidized soft carbon was immersed in HCOOHat room temperature for functionalization for 24 hours. The resultingporous, functionalized soft carbon was dried by heating at 60° C. in avacuum oven for 24 hours.

Example 3: Nanostructured Soft Carbon-Based Surface-Enabled AlkaliBattery Devices

Fully surface-enabled coin cells using functionalized soft carbon as acathode and functionalized soft carbon as a nanostructured anode (plus asmall piece of potassium foil as a potassium source implemented betweena current collector and a separator layer, Sample-1A) were made andtested. The separator was one sheet of micro-porous membrane (Celgard2500). The current collector for each of the two electrodes was a pieceof carbon-coated aluminum foil. The nanostructured electrode was aporous composite composed of 85 wt. % functionalized soft carbon (+5%Super-P and 10% PTFE binder coated on Al foil). The electrolyte solutionwas 1 M KPF₆ dissolved in a mixture of ethylene carbonate (EC) anddimethyl carbonate (DMC) with a 3:7 volume ratio. The separator waswetted by a minimal amount of electrolyte to reduce the backgroundcurrent. Cyclic voltammetry and galvanostatic charge-dischargemeasurements of the potassium cells were conducted using an Arbin32-channel supercapacitor-battery tester at room temperature (in somecases, at a temperature up to 60° C.).

As a reference sample (Sample-1-B), similar coin cells containing apiece of potassium foil as an alkali metal ion source at the anode butwithout a nanostructured carbon layer were also made and tested. This isa partially surface-enabled alkali ion-exchanging battery.

Galvanostatic charge-discharge studies of the super-battery (Sample-1-B)with such a functionalized soft carbon-based material (thickness >200μm) as a cathode active material, and those of the corresponding fullysurface-enabled battery cell (Sample-1A) have enabled us to obtainsignificant data as summarized in the Ragone plot of FIG. 10. The datawas compared to the data of the prior art symmetric supercapacitor(f-LBL-CNT/f-LBL-CNT) of Lee, et al. This plot allows us to make thefollowing observations:

-   -   (a) The fully surface-enabled, alkali ion-exchanging battery        device exhibits significantly higher energy densities and power        densities than those of the corresponding partially        surface-enabled battery under the conditions of relatively high        current densities (higher power density data points in the        plot). This demonstrates that the presence of a nanostructured        anode (in addition to the nanostructured cathode) enables high        alkali deposition rates onto the massive surface areas of the        anode during the re-charge and high alkali ion release rates        from the same massive surface areas during discharge cycles,        respectively. During fast charging and fast discharging, the        partially surface-enabled battery, having a current collector        alone (with a limited specific surface area) at the anode,        cannot provide a sufficient amount of surface area for use by        the alkali ions that try to deposit onto or release from the        limited surface area all at the same time. The whole charge or        discharge process can become surface-limited.    -   (b) The surface-enabled, potassium ion-exchanging battery device        exhibits significantly higher energy densities and power        densities than those of the prior art supercapacitor composed of        a functionalized LBL CNT anode and a functionalized LBL-CNT        cathode as described by Lee, et al (the supercapacitor has no        potassium foil as an alkali ion source).    -   (c) As mentioned earlier in the Background section, the power        density of a state-of-the-art supercapacitor is typically of        5,000-10,000 W/kg, but that of a conventional lithium-ion        battery or sodium-ion battery is 100-500 W/kg. The        surface-enabled potassium ion-exchanging battery exhibits a        power density of 143,500 W/kg (based on single-electrode        weight). This gives a power density of approximately        143,500/5=28,700 W/kg (based on the total cell weight). This        implies that the presently invented surface-enabled alkali        battery device has a power density (or charge-discharge rates)        significantly higher than the power density of conventional        electrochemical supercapacitors (despite the fact that        conventional supercapacitors are noted for their outstanding        power densities). Further, the power density of this new device        is >56-fold higher than that of a conventional lithium-ion        battery. The surface-enabled K ion-exchanging batteries have an        energy density of 262/5=52 Wh/kg, based on the total cell        weight, which is comparable to that of a modern battery (e.g.,        Ni metal hydride battery) and is 10 times higher than the energy        density of conventional supercapacitors. This is a stunning        result and it is no exaggeration to state that this        accomplishment is a revolution in the field of energy storage.

The cells of Sample-1A and Samples-1B work on the surface redoxreactions of alkali ions with select functional groups on thesurfaces/edges of aromatic rings at the cathode side (Sample-1B) and atboth the cathode and the anode (Sample-1A). These functional groups,attached to both the edge and plane surfaces of aromatic rings (smallgraphene sheets), are capable of rapidly and reversibly react withalkali ions.

The surface-enabled alkali ion-exchanging battery of the presentinvention is a revolutionary new energy storage device thatfundamentally differs from a supercapacitor since an electric doublelayer (EDL) supercapacitor relies on the formation of double layers ofcharges at the electrode-electrolyte interface. In addition, thesupercapacitor does not involve exchange of alkali ions between theanode and the cathode. This surface-enabled battery device also differsfrom conventional lithium-ion or alkali-ion batteries wherein lithium oralkali atoms (or ions) intercalate into inter-graphene spaces in agraphite particle of an anode or wherein both the anode and cathodes arebased on lithium or alkali intercalation in and out of the bulk of solidintercalation compounds.

Example 4: f-NGP Based Surface-Enabled Sodium Ion-Exchanging Batteries

For a fully surface-enabled battery, nanostructured f-NGPs prepared inExample 1 were used as both a cathode active material and as an anodeactive material. A sodium foil component was added between the anode andthe separator. The electrolyte solution was 1 M NaPF₆ dissolved in amixture of ethylene carbonate (EC) and dimethyl carbonate (DMC) with a3:7 volume ratio. For a partially surface-enabled battery, the anodecontains sodium foil as a sodium ion source (but no nanostructured NGPat the anode side) and the cathode is f-NGP. For another type ofpartially surface-enabled, sodium ion-exchanging battery, NaMnO₂ wasused as a sodium ion source implemented at the anode. Fine NaMnO₂particles were prepared by high-intensity ball milling of a mixture ofNa₂CO₃ and MnO₂ powders at a molar ratio of 1:2 for 12 hours, followedby heating at 870° C. for 10 hours, a process proposed by Qu, et al. [Q.T. Qu, et al. Journal of Power Sources, 194 (2009) 1222].

FIG. 11 shows the Ragone plot of four types of cells: a fullysurface-enabled, alkali ion-exchanging battery, a partiallysurface-enabled alkali-exchanging cell (formed of a Na metal foil at theanode as a Na ion source and a functionalized NGP cathode), anotherpartially surface-enabled, alkali ion-exchanging battery (with ananostructured NaMnO₂ anode and functionalized NGP cathode), and a priorart asymmetric supercapacitor (data re-plotted from Qu, et al). Thisasymmetric supercapacitor is composed of a conventional activated carbonanode, a NaMnO₂ cathode (micron-scaled particles), and aqueous Na₂SO₄electrolyte. These data again demonstrate the superiority of thepresently invented surface-enabled, metal ion-exchanging approach interms of providing both a high power density and high energy density. Itmay be noted that the asymmetric supercapacitor of Qu, et al does notmake use of a nanostructured cathode or anode and does not involve theexchange of sodium ion between the anode and the cathode.

Example 5: Organic Poly(2,5-dihydroxy-1,4-benzoquinone-3,6-methylene)(PDBM) and Nanostructured NGP-Supported PDBM

The PDBM material was synthesized with the following procedure: One gramof 2,5-dihydroxy-1,4-benzoquinone (7.14 m mol) was dissolved in 75 ml ofwarm glacial acetic acid. An approximately 37% aqueous formaldehydesolution (3 ml) was then added and the resulting mixture was leftstirring for 48 h at room temperature. The precipitate was thencollected by filtration, thoroughly washed with water, and dried underhigh vacuum to yield the desired polymer (PDBM) as a yellow solid(approximately 0.85 g).

Two types of electrodes were then prepared. One involved mixing PDBMsolid with carbon black (CB) particles and the other involved combiningPDBM with graphene oxide. As an example, an amount equal to 0.7 g of thePDBM was dissolved in 100 ml propan-2-ol to form a polymer solution.Non-porous CB particles were then dispersed in the polymer solution toform a suspension at a PBDM/CB weight ratio of 80/20. Upon removal ofsolvent in a vacuum oven, PDBM was found to precipitate out asindividual solid particles (0.2-0.8 μm in diameter) well mixed with CBparticles. On a separate basis, graphene oxide (mostly single-layergraphene sheets supplied by Angstron Materials, Inc., Dayton, Ohio) wasdispersed in a similar polymer solution to form a suspension(PBDM/graphene ratio of 95/5). Upon removal of solvent, PDBM was foundto stick to the graphene surface as a thin-film coating (possibly amono-layer of polymer chains physically attached or chemically bonded tographene oxide). The resulting graphene oxide-supported PDBM was thenannealed at 250° C. for 3 hours to thermally reduce graphene oxide tosome extent for the purpose of recovering some electronic conductivity.

Coin cells similar to those discussed in Example 3 were prepared andsimilarly evaluated. The results are summarized in the Ragone plot ofFIG. 12(B), which clearly show that the fully surface-enabled batterydevice based on an NGP-supported PDBM polymer anode and a f-NGP cathodeperforms much superior to the corresponding partially surface-enabledbattery containing a PDBM-CB composite anode and an f-NGP cathode. Inboth battery devices, sodium powder was added as a sodium ion source atthe anode. The PDBM particles in this latter device are submicron indiameter, requiring sodium ions to diffuse in and out of the particles.In contrast, the single-layer graphene oxide appears to be capable ofinteracting with PDBM chains in such a manner that these chains arewell-dispersed on massive graphene surfaces (with a specific surfacearea typically in the range of 300-1,550 m²/g, albeit theoretically upto 2,670 m²/g). In other words, it appears that the precipitation ofPDBM chains during solvent removal was constrained by the graphene oxidesurface and was prevented from forming bulk PDBM crystal particles. Sucha graphene surface-supported PDBM structure makes it possible for theanode operation to be surface-enabled or surface-mediated. The cathodeoperation (f-NGP) is also surface-enabled. By combining PDBM withgraphene oxide to obtain the graphene-supported PDBM, we obtain a muchbetter surface-enabled sodium ion-exchanging battery device in terms ofboth the energy density and power density at comparable currentdensities.

It seems that enolation is a possible reaction of carbonyl double bonds,which can be stabilized by conjugated structures. Enolation makes itpossible for sodium ions to be captured or released reversibly at thepositions of oxygen atoms when the carbonyl groups are reduced oroxidized. In the reduction process of PDBM, each carbonyl group possiblycan receive one electron and capture one Na ion to form sodium enolate,and the Na ions can be released in the reverse oxidation process, asillustrated in FIG. 12(A).

Example 6: Preparation of Nanostructured, Functionalized ActivatedCarbon (f-AC) and f-AC Based Surface-Enabled, Alkaline-Earth MetalIon-Exchanging Battery

Activated carbon (AC, from Ashbury Carbon Co.) was treated with an acidsolution (sulfuric acid, nitric acid, and potassium permanganate at aratio of 4:1:0.05) for 24 hours for the purposes of opening up the gatesto facilitate liquid electrolyte entry into the interior of AC particlesand to impart functional groups to the surfaces (including edges) of thearomatic rings or small graphene sheets inside AC. Upon completion ofthe reaction, the mixture was poured into deionized water and filtered.The treated AC was repeatedly washed in a 5% solution of HCl to removemost of the sulfate ions. The sample was then washed repeatedly withdeionized water until the pH of the filtrate was neutral. The slurry wassubjected to further functionalization in formic acid at 25° C. for 30minutes in an ultrasonication bath. Subsequently, dip-coating was usedto obtain thin films of chemically functionalized activated carbon(f-AC) with a thickness of typically between 20 and 150 μm coated on asurface of an aluminized carbon layer as a current collector. Such anelectrode was used as an anode and a functionalized NGP material wasused as a cathode, with a predetermined amount of calcium powderimplemented between a porous separator and one electrode as analkaline-earth metal ion source. The resulting device is asurface-enabled, alkaline-earth metal ion-exchanging battery (calciumion as an example). The electrochemical performance of such asurface-enabled, calcium ion-exchanging battery is shown in FIG. 13.This battery device exhibits exceptional power density and energydensity.

Example 7: Surface-Enabled, Transition Metal and Other MetalIon-Exchanging Batteries

In this example, a transition metal (Zn) and an example (Al) of othermetals in the periodic table of elements are considered. In both cases,NGP is used as a nanostructured anode and f-NGP as a nanostructuredcathode. For the aluminum ion-exchanging battery, the electrolyte usedwas LiPF₆ and Al(BF₄)₃ (at a ratio of 1:4) dissolved in EC/EMC/MB (at aratio of 1:1:8), where EC=ethylene carbonate, EMC=ethyl methylcarbonate, and MB=methyl butyrate. For the zinc ion-exchanging batterydevice, the electrolyte was zinc borofluoride (Zn(BF₄)₂) dissolved inthe same solvent mixture. The electrochemical performance of these twosurface-enabled, Zn ion- and Al-ion exchanging battery devices is alsosummarized in FIG. 13. These battery devices again exhibit exceptionalpower density and energy density.

The above examples, along with chemical analysis results, suggest thatthe surfaces (including edges) of nanostructured materials (such asnanographene, porous hard carbon, carbon nanotubes, etc), with a properchemical functionalization treatment, are imparted with functionalgroups that are capable of rapidly and reversibly react or interact witha wide range of metal ions to form surface redox pairs or chemicalcomplexes, as illustrated in FIG. 14.

The following conclusions may be drawn from the above discussion:

-   (1) The instant invention provides a revolutionary energy storage    device that has or exceeds the best performance features of both the    supercapacitor and the lithium ion battery.-   (2) The device can deliver a power density higher than that of the    best supercapacitor by a factor of 5-10 and an energy density higher    than that of the best supercapacitor by a factor of 20.-   (3) The presently invented surface-enabled, metal-ion exchanging    battery device using a functionalized nanostructured carbon (such as    porous disordered carbon, CNT, and NGP) as an anode and as a cathode    also exhibits a power density of approximately 10-60 times higher    than that of conventional lithium-ion batteries.-   (4) These surface-enabled batteries can be re-charged in seconds, as    opposed to hours for conventional lithium ion batteries.-   (5) State-of-the-art Li-air cells can only be operated for a small    number of cycles (typically <50 cycles) and the best lithium-ion    batteries only for <1000 cycles, but our surface-enabled devices are    capable of cycling for tens of thousands or hundreds of thousands of    cycles.-   (6) This new surface-enabled, metal ion-exchanging battery device is    patently distinct from the conventional supercapacitor that operates    on the electric double layer (EDL) or pseudo-capacitance mechanism.    The supercapacitor does not involve the exchange of ions between an    anode and a cathode during charging and discharging.-   (7) This new surface-enabled, metal ion-exchanging battery device is    patently distinct from the conventional lithium-ion, sodium-ion, or    potassium-ion batteries because the anode and/or the cathode    (typically both electrodes) in these conventional batteries rely on    intercalation (solid-state diffusion) of metal ions in and out of    the bulk of electrode active material particles, which is a    painfully slow process.-   (8) It may be noted that most of the metal ions (e.g. Ca²⁺, Zn²⁺,    Al³⁺, etc) are relatively large in size (all significantly greater    than the size of Li⁺) and it would be difficult or impossible to    find an anode intercalation compound and a cathode intercalation    compound that are amenable to insertion (intercalation) and    extraction (de-intercalation) of these large metal ions into/from    the interior of these solid compounds. The presently invented    surface-mediation or surface-enabling approach obviates the need for    such a solid state diffusion. This strategy enables those divalent,    trivalent, or other multivalent metal ions (that have more than one    charge unit per ion) to be used as a charge carrier being shuttled    between an anode and a cathode. This is very significant since, as    an example, each exchange of an Al³⁺ involves the delivery of three    electrons, not just one.-   (9) This surface-mediation or surface-enabling approach basically    provides a safe, fast, and tentative but stable mechanism to “store”    or capture all kinds of metal ions (atoms) on the surface of a    nanostructured or functional material, as opposed to having to form    a metal oxide in the electrolyte or cathode of a metal-air battery,    or having to form metal sulfide (e.g. lithium sulfide or    polysulfide) in the electrolyte or cathode of a metal-sulfur    battery. The reverse reactions (reduction) of these metal-air and    metal-sulfur cells (or metal-halogen, metal selenium cells, etc) are    notoriously slow or not considered possible even with the assistance    from expensive electro-catalysts.-   (10) The presently invented surface-enabled, metal ion-exchanging    battery device represents a truly major breakthrough or    revolutionary energy storage technology that has tremendous utility    value. The commercialization of this technology will have a major,    highly positive impact to the environment and society.

We claim:
 1. A partially or fully surface-enabled, metal ion-exchangingbattery device comprising (a) a cathode, (b) an anode, (c) a porousseparator disposed between said cathode and said anode, and (d) anelectrolyte in physical contact with said cathode and said anode,wherein said electrolyte comprises a metal ion salt and a metal ion thatis exchanged between said cathode and said anode during an operation ofsaid battery device and said metal ion or metal ion salt is selectedfrom transition metals, wherein at least one of said cathode and saidanode comprises therein a source of said metal ion prior to a firstcharge or a first discharge cycle of the battery device and at least thecathode comprises a functional material having a surface-borne metalion-capturing functional group or a nanostructured material having ametal ion-storing surface in direct contact with said electrolyte toreversibly capture or store said metal ion during charge-dischargeoperations of said battery, wherein the functional material comprisesnanographene selected from single-layer graphene sheets or multi-layergraphene platelets, wherein said transition metal is selected fromscandium (Sc), titanium (Ti), vanadium (V), chromium (Cr), manganese(Mn), iron (Fe), cobalt (Co), nickel (Ni), zinc (Zn), cadmium (Cd), andcombinations thereof.
 2. The partially or fully surface-enabled, metalion-exchanging battery device of claim 1, wherein said electrolyte alsoincludes a metal ion or metal ion salt selected from alkaline-earthmetals consisting of beryllium (Be), magnesium (Mg), calcium (Ca),strontium (Sr), barium (Ba), combinations thereof, and theircombinations with lithium, and said electrolyte also includes a metalion selected from lithium ion, an alkaline metal ion, and combinationsthereof.
 3. The battery device of claim 1, wherein said transition metalis selected from titanium (Ti), vanadium (V), chromium (Cr), manganese(Mn), iron (Fe), cobalt (Co), nickel (Ni), zinc (Zn), and combinationsthereof.
 4. The battery device of claim 1, wherein the metal ion salt isan alkali metal, alkaline-earth metal, transition metal, aluminum (Al),gallium (Ga), indium (In), tin (Sn), lead (Pb), or bismuth (Bi), andsaid metal ion salt is dissolved in an organic solvent.
 5. The batterydevice of claim 1, wherein the metal ion salt is selected from a lithiumsalt, sodium salt, potassium salt, calcium salt, magnesium salt, zincsalt, titanium salt, transition metal salt, aluminum salt, lithiumperchlorate (LiClO₄), sodium perchlorate (NaClO₄), potassium perchlorate(KClO₄), lithium hexafluorophosphate (LiPF₆), sodium hexafluorophosphate(NaPF₆), potassium hexafluorophosphate (KPF₆), transition metalhexafluorophosphate, aluminum hexafluorophosphate (Al(PF₆)₃), lithiumborofluoride (LiBF₄), sodium borofluoride (NaBF₄), potassiumborofluoride (KBF₄), calcium borofluoride (Ca(BF₄)₂), aluminumborofluoride (Al(BF₄)₃), transition metal borofluoride, alkaline-earthmetal borofluoride, lithium hexafluoroarsenide (LiAsF₆), alkali metalhexafluoroarsenide, transition metal hexafluoroarsenide, aluminumhexafluoroarsenides, lithium trifluoro-metasulfonate (LiCF₃SO₃),bis-trifluoromethyl sulfonylimide lithium (LiN(CF₃SO₂)₂), andcombinations thereof.
 6. The battery device of claim 1, wherein saidelectrolyte comprises liquid electrolyte or gel electrolyte.
 7. Thebattery device of claim 1 wherein said electrolyte is an aqueouselectrolyte.
 8. The battery device of claim 1, wherein said electrolytecomprises a solvent selected from ethylene carbonate (EC), dimethylcarbonate (DMC), methylethyl carbonate (MEC), diethyl carbonate (DEC),methyl butyrate (MB), ethyl propionate, methyl propionate, propylenecarbonate (PC), γ-butyrolactone (γ-BL), acetonitrile (AN), ethyl acetate(EA), propyl formate (PF), methyl formate (MF), toluene, xylene, methylacetate (MA), and combinations thereof.
 9. The battery device of claim1, wherein at least one of said cathode and said anode comprises saidfunctional material having a functional group that reversibly reactswith said metal ion of claim 1, forms a redox pair with said metal ion,or forms a chemical complex with said metal ion.
 10. The battery deviceof claim 1, wherein both said cathode and said anode comprise saidfunctional material having a functional group that reversibly reactswith a metal ion, forms a redox pair with a metal ion, or forms achemical complex with a metal ion.
 11. The battery device of claim 1,wherein at least one of said cathode and said anode comprises ananostructured functional material having a specific surface area from100 m²/g to 1,500 m²/g to store or support metal ions or atoms thereon.12. The battery device of claim 1, wherein said metal ion sourcecomprises a metal chip, metal foil, metal powder, surface stabilizedmetal particles, or a combination thereof.
 13. The battery device ofclaim 1 wherein said functional material further comprises single-walledor multi-walled carbon nanotubes.
 14. The battery device of claim 1wherein at least one of said functional materials has a functional groupselected from COOH, ═O, —NH₂, —OR, or —COOR, where R is a hydrocarbonradical.
 15. The battery device of claim 1 wherein said electrolytefurther comprises lithium ions and/or said exchanging metal ion sourcefurther comprises a Li ion source.
 16. The battery device of claim 1wherein said electrolyte comprises an alkali metal salt-doped ionicliquid.
 17. The battery device of claim 1 wherein said device providesan energy density of no less than 100 Wh/kg, based on the electrodeweight, and a power density no lower than 10 Kw/kg, based on theelectrode weight.
 18. A partially or fully surface-enabled, metalion-exchanging battery device comprising (a) a positive electrode(cathode), (b) a negative electrode (anode), (c) a porous separatordisposed between said cathode and said anode, and (d) an electrolyte inphysical contact with said cathode and said anode, wherein saidelectrolyte contains a transition metal ion that is exchanged betweensaid cathode and said anode during an operation of said battery device;wherein at least one of said cathode and said anode contains therein asource of said metal ion prior to a first charge or a first dischargecycle of the battery device and at least the cathode comprises afunctional material having a surface-borne metal ion-capturingfunctional group or a nanostructured material having a metal ion-storingsurface in direct contact with said electrolyte to reversibly capture orstore said metal ion during charge-discharge operations of said battery,wherein said nanostructured material comprises a nanostructured orporous disordered carbon material selected from a soft carbon, hardcarbon, polymeric carbon or carbonized resin, mesophase carbon, coke,carbonized pitch, carbon black, activated carbon, partially graphitizedcarbon, and combinations thereof, wherein said transition metal ion isselected from scandium (Sc), titanium (Ti), vanadium (V), chromium (Cr),manganese (Mn), iron (Fe), cobalt (Co), nickel (Ni), zinc (Zn), cadmium(Cd), and combinations thereof.
 19. The battery device of claim 18wherein said disordered carbon material is formed of two phases with afirst phase being graphite crystals or stacks of graphene planes and asecond phase being non-crystalline carbon and wherein said first phaseis dispersed in said second phase or bonded by said second phase andsaid disordered carbon material contains less than 90% by volume ofgraphite crystals.
 20. A partially or fully surface-enabled, metalion-exchanging battery device comprising (a) a positive electrode(cathode), (b) a negative electrode (anode), (c) a porous separatordisposed between said cathode and said anode, and (d) an electrolyte inphysical contact with said cathode and said anode, wherein saidelectrolyte contains a transition metal ion that is exchanged betweensaid cathode and said anode during an operation of said battery device;wherein at least one of said cathode and said anode comprises therein asource of said metal ion prior to a first charge or a first dischargecycle of the battery device and at least the cathode comprises afunctional material having a surface-borne metal ion-capturingfunctional group or a nanostructured material having a metal ion-storingsurface in direct contact with said electrolyte to reversibly capture orstore said metal ion during charge-discharge operations of said batterydevice, wherein said functional material is selected from the groupconsisting of poly(2,5-dihydroxy-1,4-benzoquinone-3,6-methylene),Li_(x)C₆O₆, wherein 1≤x≤3, Li₂(C₆H₂O₄), Li₂C₈H₄O₄ (Li terephthalate),Li₂C₆H₄O₄(Li trans-trans-muconate),3,4,9,10-perylenetetracarboxylicacid-dianhydride (PTCDA) sulfidepolymer, PTCDA, 1,4,5,8-naphthalene-tetracarboxylicacid-dianhydride(NTCDA), benzene-1,2,4,5-tetracarboxylic dianhydride,1,4,5,8-tetrahydroxy anthraquinon, tetrahydroxy-p-benzoquinone, andcombinations thereof, and wherein said functional material is optionallycombined with or optionally supported by a nanostructured materialselected from nanographene, carbon nanotube, disordered carbon,nanographite, metal nanowire, conductive nanowire, carbon nanofiber, orpolymeric nanofiber, wherein said transition metal ion is selected fromscandium (Sc), titanium (Ti), vanadium (V), chromium (Cr), manganese(Mn), iron (Fe), cobalt (Co), nickel (Ni), zinc (Zn), cadmium (Cd), andcombinations thereof.
 21. The battery device of claim 1 wherein saiddevice provides a power density no lower than 10 Kw/kg, based on theelectrode weight.